Full versus Half Sibling DNA Matches

Recently I was asked whether there is a way to tell a full sibling from a half sibling. Sometimes the total centimorgans are low for one but high for the other. You expect to share about 2550 cM with a full sibling and 1700 with a half sibling; so which is it if you share 2100 cM?

The answer is that full siblings will share many fully identical regions (FIRs), over about 25% of their chromosomes. Half siblings will have no FIRs of any significant size. The exception being some small ones if their parents are from the same population group but still far far fewer than a full sibling.

Here is a comparison of my first eight chromosomes with my brother made at GEDmatch. The green bars are where we are fully identical, in other words we got the same segment of DNA from each of our parents there.

GEDmatch comparison of me and my brother

GEDmatch comparison of me and my brother (full siblings)

You can click on the image to see the entire display at GEDmatch that this was made from.

The old 23andme used to show these FIRs and HIRs in the “Family Traits” display when you selected Genome-Wide Comparison. You can see my brother and mine on this page: http://blog.kittycooper.com/about-me/our-dna-test-results/autosomal-dna-picture/

I have not been able to find this tool in the new 23andme experience, so I guess it is gone. If anyone finds it let me know. There is a new way it shows traits under Share and Compare and many new traits are listed. For example, most of my family has a widow’s peak. [UPDATE 5 Apr 2017: FIRs are now back, they are shown when you compare DNA relatives in the chromosome browser.]

So how to get the FIRs from GEDmatch? In the one-to-one comparison be sure to you click “Yes” next to the question “Show graphic bar for each Chromosome?” You will get a display of every chromosome (not in scale to each other) and the numbers that go with the matches as well as the blue bars for each half matching region (HIR) and the green bars for the FIRs. [UPDATE: you can also click next to “Graphic Only” to get just the picture]

A word of warning, double first cousins, where two brothers married two sisters, will also have many FIRs (about 12.5%) but their centimorgan count will look like half siblings.

Use the article at ISOGG on autosomal statistics as your reference guide for the expected centimorgans for various relatives: http://www.isogg.org/wiki/Autosomal_DNA_statistics


UPDATE 3 jan 2017: Now that you can look at just the image at GEDmatch I thought it might be useful to look at a pair of known half siblings (click for a larger image)… no large green bars.


Half Siblings at GEDmatch (click for full image)

546 thoughts on “Full versus Half Sibling DNA Matches

Click here to add your thoughts at the end of the comments
  1. Half siblings have the same father or the same mother. Therefore they most likely will share some fully identical regions (FIRs) from their common parent. How do you explain your comment that “Half siblings will have no FIRs of any significant size.”?

    • Carl,
      Perhaps I should have defined my terms better. Fully identical means a segment with a match on both the paternal and maternal chromosomes.

      You have 23 pairs of chromosomes, 23 from each parent. So a half sibling will only share DNA with you from one parent, thus half indenticall in those places. Full siblings will have sections where they got the same DNA as each other from each parent thus fully identical sections.

      See if this explanation of FIRs at ISOGG helps

      • I just got my test results back and I’m having a little trouble understanding them so does 45% mean that me and the alleged brother are half siblings or not

        • Did you get a reply? I have a similar situation 40% DNA match with a half sibling. Would you share what you discovered about this?

          • Bonnie – same answer, likely a full sib but look at the image for FIRs. A half sib would be only 25% but if the the other parents are related it could be higher.

        • Where did you test – better to look at the total cMs and whether there are any FIRs.
          45% at 23andme is a full sib, a half sib would share about 25%

          • Hi,

            I have results that state 24.7% however, it states that this percentage is the likelihood we are half siblings, not the amount of DNA we share. They stated because I had extra markers tested it is less likely that we are related but its not enough to totally deny the relationship. I am very confused. We went through Paternity USA

          • Cheryl
            So sorry, I cannot help you with that test. Call their customer support and ask your questions there.

      • Ms Kitty

        I’m in quite a Delima., I had Ancestry DNA test done to research my family. I found 2 girls with 1600 and 1700 centrimorgans to match me. Ancestry said they could be Looks like they are my 1-2 sisters. How can I be sure?

        Cindy K

        • Hello Cindy, Kitty has explained a few scenarios where this could be the case. One, they really are your half-siblings! Those centimorgans are pretty high. Two, they are close cousins that may have married other cousins close to you. Three, one of your parents may have had a twin that no one knows of? 🙂 Now that would be interesting!

          • Hi Reginald,
            I have a similar issue. My brother (who I believed to be my full sibling) has come in as a close family to first cousin which apparently indicates he is in fact my half brother. The DNA indicates 1,902 centimorgans shared across 56 DNA segments. So is this conclusive that we are infact half siblings and not full.


          • Hello Reginald, what is the relationship between myself and this person who has 1,900 cm 68 segments. He is younger than me.

      • If I have an paternal uncle showing up as my 1-2 cousin on Ancestry does that indicate a paternal anomaly? Both my mother’s siblings show up as my aunt and uncle.

        • Cori –
          If you are from an endogamous population like Ashkenazim or Polynesians, etc then Ancestry can remove segments it deems population specific making the total smaller than it is. Best to both upload to gedmatch genesis and compare there
          Look at the total cMs and use this calculator to see if they are not as expected:

      • What does mean if Two people have the same 2,293cm number would they be brothers and sisters or half

        • Curtis,
          They could be either but 2 to 1 that it is a full sib. Use this calculator to see the possibilities:
          To figure out which, best to look at the fully identical segments as described in this post.
          However you may be able to figure it out based on whether they share both your maternal and paternal relatives or just one side …

    • Kitty, I just completed DNA testing for half sibling sharing a father (Trying to determine my bio dad is). I used TestMeDNA, they use LabCorp and the results came out with Inconclusive and show a percentage, a male with 32.9 percent and a female 32.4%. Their dads are brothers, yet, my match is almost identical to both. Not sure I understand that, other than the male with both XY conclusion may be stronger. My belief is that the female is my half sister and her father being the same as mine. They said anything under 91% they give an Iconclusive as the answer. I saw no cMs or anything mentioned in your blog to compare. My test results show things like HB1. HS1 D3S1358. D7S820 vWA FGA D8S1179 DS21S11 D18S51 D5S818. D13S317. D16S539 Second set THO1. TPOX. CSF1PO. AMEL. Penta D. F13A01. F13B LPL. Penta E. FESFPS. and last box. HB1. HS1 PI. It also says the sibling indeedx for Half siblings is 0.49-1. This value is inconclusive Are you able to help me figure this out? Did I take the wrong DNA test? Thank you in advance

      • Sorry I missed this question
        Yes that is not the type of test I discuss on this blog, so I cannot be of help with it
        Go to dnaadoption.com for advice on finding your dad or DNA detectives on Facebook

      • Hi Bonnie,
        I did a test with testmeDNA to see if i had a half sibling, and it also came back inconclusive. I am confused as well. My sibling index was 1.19. to 1. I’m not sure what to think of these results.

      • I’m having the same issue , my half brother and I supposedly share the same dad and we definitely have different moms and my dna results came back 33.6% (0.50) for the half sibling part so idk if mines is inconclusive as well , were you able to get the answer you was looking for with that percentage ???

        • Angela –
          If you tested with 23andme,Ancestry, FamilyTree DNA, or MyHeritage and have 33.6% then according to the DNApainter calculator you are full siblings but it sounds like you used a different compny that is not a full genome test in which case I cannot help you. Ask their support desk.

          • Hello Kitty I used Ancestry. com DNA here are my results 2161 CM 156 CM over 47 Segments 38% – 44% is this half sister or full sister Ancestry says 100% sister. Thank you

          • Tami –
            You have to both upload to GEDmatch and compare your results there as shown above to be sure.

    • this woman claiming she has my child coherced my twins mother into a sibling dna test. it came back 98% match to father…. is this accurate?

      • Chad –
        I don’t follow what you are saying but it sounds plausible. Having a child can be a wonderful experience.
        But the test you are talking about is not my area of expertise, I work with AncestryDNA, 23andme, MyHeritage, etc personal genome tests which are amazingly accurate for close family relationships.

        • Kitty,

          So I just done a sibling test to confirm if my kids are full siblings or not ( They father and other guy are brothers) .. So I got the results today which said the chances of them being full siblings are 52 percent?

          Does this mean they are full siblings or not ? Having the same mum and da do expected it to be alot higher percentage?

  2. Interesting, didn’t realize double 1st cousins could produce that.

    The first half-brother I got tested turns out we share 1602.5cM. The other half-brother I tested we share 1981.8cM.

    When my mother’s new found sister (actually my mother is the new found sister) asked to get DNA tested I was happy. But her reason was to see if she was a half-sister rather than a full-sister as been believed by the entire family. My aunt felt that her father was not her biological father. I thought that would be easy to determine.

    Initially I saw the results at FTDNA where they came up predicted as full or half sibling sharing 2182.92cM, about the same as what you mentioned in your example. I thought since my aunt was questioning her father, it would be easy to tell by their X. It was actually confusing!

    I immediately transferred over to GEDmatch (the next day since there were issues at the time with GEDmatch) and saw that they shared 2084.8cM, not much of a difference. But still the X chromosome was confusing to me. I expected either a full 196cM or so on the X or significantly less.

    Luckily after doing a comparison on the autosomes it was obvious, although I expected several FIR but in small amounts, turns out they really are half-sisters and my aunt was right.

    You’ll see what I mean by confusing with the X in the diagram.


  3. Thank you Kalani for sharing the GEDmatch image for half siblings in an endogamous population!

    The small FIRs are as expected since the farhers are related, albeit distantly multiple times.

    You were right to think the X would tell you. people sharing the same father get the same unrecombined X from him so a solid blue bar on their X as per this article http://blog.kittycooper.com/2014/03/how-can-the-x-chromosome-help-with-maternal-versus-paternal/

    Your sample has some tiny breaks on the X (chr 23). Possibly since the mother’s parents would have been distantly related, she had many FIRs on her X leading to what looks like less recombination

    • Thanks Kitty for that. I couldn’t understand why the X would look like that. At FTDNA, it looked differently of course, looked more like slices were taken out.


      I never gave it any thought that my mother’s maternal grandparents may have been distantly related multiple times which is also a possibility. Although my mother still has two more half-brothers alive who could test, both have different fathers and probably from my aunt too, it would be interesting to see how much X they all share with each other.

      • Kalani
        It would be very interesting. Please let me know. The X fascinates me. Will I see you at Jamboree?
        One mistake I see people make is assumin a small X match is on the same line as the large autosomal match. This really does not have to be so, especially in even mildly endogamous populations!

  4. Interesting blog.

    I just read your message on the Newbie group and thought I might learn something.

    We are trying to determine if two women who have the same mother, might also have 2 brothers as fathers. It’s so confusing. I was hoping that xDNA would help determine this. I’m posting a link to the GEDMATCH data that I produced for them. I could really use some help figuring this out.



    • I think CeCe answered you on the Newbies list. The lack of green bars makes it unlikely. Look also at their autosomal DNA as well. Again there will be green bars if the men are brothers.

      • I had a sibling dna test done and really am not sure of the results.The full sibling index is 1.00 and half sibling index is 1.25 does this mean we are more likely half sisters than full sisters?

        • Same mother-
          Siblings as fathers.
          The resulting children would be 3/4 siblings, half-siblings on one side and cousins on the other. Not full siblings, not half-siblings.
          They WOULD share fully identical regions, as they could happen to have gotten the same DNA from their dads and their moms in the same place. And all. About 12.5%, I think. (i think.) They’d share on average 37.5% DNA. The amount of FIR would probably distinguish them from half-siblings, but not full siblings. Two 3/4 siblings can share a high amount of DNA, putting them on the low end of the full sibling range.
          *ahem.* If there are no green bars, meaning very little FIRs, (or none,) they’re probably not 3/4 siblings. Or full siblings. Most likely half-siblings.

          this is the end of my rant~!

  5. Thanks,

    It just dawned on me that it would be difficult to see if two brothers fathered half sisters using xDNA since they got their xDNA from recombined xDNA from their mother. I assume that it recombines each time a new child is conceived. So we can only prove the 1/2 sibling relationship based on 28% shared autosomal.

    I’m learning more every day.

  6. Thanks for this. My half brother has tested and is waiting for his results (from AncestryDNA). I look forward to explaining to him why I’d like him to export his results to GEDMatch (or FTDNA) so I can see the results on a chromosome browser. Since I have no first cousins on my dad’s side, this will be a great help going forward in my DNA learning.

  7. Hello Kitty:

    My half sister is showing as sharing 1484 cms. Ancestry is showing us as first cousins as well as Gedmatch, but there is no way that she is my first cousin because my dad dated her mom.

    • I have a similar issue sort of. When comparing my DNA in GED match, someone came up with 1293 as a score saying first cousins. The issue with that is that all of my parents siblings lived in CT and were under 18 and my mother and father were split at the time but lived near where the person was born and raised. Further we added each other on FB and he is a dead ringer for my father and his brothers. Wondering if the amounts are lower for opposite sex half siblings because honestly, there are no mystery children that would be siblings to my parents that would have been old enough to parent a child.

      • That is just below the bottom of the range for a half sibling but not impossible if you are tested at different companies. Can you get more paternal side relatives to test to help narrow this down? Get in touch with your new “cousin” and offer to help. Adoptees are told to be circumspect with mentioning that because many will turn away at that news. Sounds like you are not one to do so! Congrats

      • Did you find out if y’all were 1/2 siblings or still cousins. I’m
        Having same issue. We’re at 1284. We have higher percentages in some areas that my 1/2 sister I know about.

  8. Troy
    That total is a little bit low for half siblings but certainly possible and very high for first cousins. Ancestry and GEDmatch have no way of knowing which it is, they are guessing from the match size. Look at the statistics here to see all the possibilities:
    There is no easy way to prove a half sister to a half brother who share a Dad. However siblings will usually have larger segments of matches (50/60/70/80 cM) than first cousins. So look at those. What are the largest two segments in the match?
    If there are other possible relationships, see if you can disprove those in the DNA.

  9. Thanks for your response. The largest segments are 165, 136, 131, and 108. I also have a few that are in the 70s and 80s. My dad told me that it was a possibility that she was his daughter. I feel 95% sure that she is but I wanted to be sure.

    Thanks again!

  10. Thanks, but I guess I need to know how you can tell from the length of the centimorgan? Sorry for asking so many questions.

    • Only very close family will share such large segments as you report. A cousin will not have many segments greater than 40cM. Only a sibling would share that many big pieces with you.

      • Me and my “1st cousin” share 43 segments
        75.7 largest segment
        1284.6 cm
        73.145 pct snp full identical
        Could we be 1/2 siblings? We have some higher and more in common than my 1/2 sisters. My dads deceased and so is his brother. Definetly more like time line and area leads up to my dad. He was adopted so we don’t have much else to go off except our dna test.

  11. If half siblings txt at around 1700 cm to 2000 .. thats a little daunting . my mothers brother and i share 2000 cm. a little strange that we had such a high number and my half sister shares 2267. I guess its confusing.

    • Linda
      Autosomal DNA has very few absolutes… is it at all possible that you are from an endogamous population group? That would explain these higher numbers. Also if your parents are distantly related.

  12. hello kitty i am doing a DNA testing for court for half sibling. My dad is deceased and the girl he raised which is not his daughter and me which i am his son are orderd by the court to do the half sibling test . question is how accurate is dna testing and will it show that we dont have the same father in the result. thank you for your response.

    • Muellew –
      Sorry for the late response but the reply I wrote on my phone today got lost somehow.
      If you are testing to see if you are closely related or not at all, then an autosomal DNA test, like Ancestry.com DNA or Family Tree DNA will answer your question. But you may need to upload the results to GEDmatch.com or DNA.land to see the details and confirm.
      Half siblings look very much like uncle/niece or grandparent/grandchild, so if those relationships are possible you may need further testing, either of cousins or a more traditional sibling test using STRs.
      However this adoptee, whose opinion I totally trust, suggests that those STR tests are not useful here:

    • Muellew – the courts will set up your ‘court ordered’ testing. But without a parent to compare to, I don’t see how they will be able to do this, as with my own paternal testing, each child and each parent had to submit DNA (done by buccal swab test)
      For more information on the legality of this, see the link: https://dnatesting.com/paternity-testing-without-the-father/

      But to add in my own .02 – both have done via Ancestry & FTDNA – my sons whom have different fathers, do show they are closely related. Both companies ‘suggest’ they are half siblings/cousins. And of course, because I also have my testing done at both companies, they both show me as their parent. So conclusive on our end – they cannot say I am ‘NOT’ their mama (as a pun towards Maury)

  13. thank you so kitty for your resopnse. Will the half sibling DNA testing show if we are related or not right Kittyeee?
    thanks again.

    • Sorry muellew, my expertise is for personal genome tests. I have no experience using those other tests, they were suggested as an alternate by another genetic genealogist

  14. I was contacted by an adopted girl who shares DNA with me. At first we thought she was a cousin according to ancestry.com, but according to timeline of her birth, we are thinking she may be the daughter of my half sibling I didn’t know about. We share 1106 cm and largest is 152. Is this possible that she is my niece rather than cousin

    • Tami, Yes either relationship is possible based on those cMs. Do you have other family members who are tested? Can you get more of them to test? can you ask, delicately, around in your family? If you have uploaded both kits to Gedmatch I would take a quick look for you, send me the kit numbers via my contact form

  15. Hi kitty…I just downloaded mine and my suspected to be half siblings/cousin’s dna in gedmatch. It’s was 1,377 cM with the largest segment being 128.1 cM. Would you say we were half siblings or first cousin.

    • Shannie –
      That is not enough information. It could be either or an aunt/niece relationship. Is the second largest segment also over 100? Are there any full chromosomes matching? How much X?
      Try the calculator at DNAadoption.com and I emailed you so that you can send me the kit numbers.
      The only way to be sure is to test more relatives of the non adoptee. For example, test maternal and paternal first cousins. If both match then aunt/niece.

  16. X and O’s to show just how confusing it can be but if you take the time
    to figure it out it can add a lot to your research.

    Some real life X DNA matches between half siblings, Full siblings
    half niece, full niece, half 1st cousin.

    K, D, J, G, and S’s deceased mother all have same mother
    G has different father
    K has different father than G and different than D,J, and S’s mother
    D, J, and S’s deceased mother all have same father
    D, J, and G are male

    S=Full niece to D,J, through deceased full sister, half niece to G and K

    Dd=half nephew to D and J and S’s mother (1/2 1st cousin to S) through
    D and J’s father and S’s grandfather. Dd’s mother has same father as D, J, S’s deceased mother but different mother.

    D-S X 128,500,991 133,915,684 5.1 541
    J-S X 128,500,991 133,968,536 5.2 246
    G-S X 128,500,991 133,968,536 5.2 247
    K-S X 127,872,771 134,326,312 6.2 652

    X 2,710,157 12,647,010 26.4
    X 13,142,754 44,399,427 49.8
    X 123,194,758 146,604,866 38.5
    X 10,024,609 44,399,427 54.5
    X 123,194,758 146,604,866 38.5
    X 10,024,609 44,399,427 54.5
    X 123,194,758 146,604,866 38.5
    X 13,173,093 151,050,290 160.8
    X 13,173,093 154,488,536 167.7
    X 118,624 151,054,252 189.1

    X 850,802 21,936,384 38.9
    X 38,883,698 154,088,731 128.7

  17. So I did the ‘are your parents related’ on gedmatch and the outcome is this:

    Largest segment = 83.1 cM
    Total of segments > 7 cM = 979.0 cM
    Estimated number of generations to MRCA = 1.9


    Largest individual segment of SNPs with greater than 500 matches: 7.0 cM

    Total autosomal SNPs in segments with greater than 500 matches: 183595

    No full matches, only half matches, and looking at the chromosome picture it looks like a good 25-30% is shared. So what does this mean? First cousins? Double first cousins? Randomly shared lines? Trying to figure it all out.

  18. That is the largest I have ever seen from are your parents related. I need to consult with a few other experts but to me it looks like your parents are half siblings or uncle/aunt and niece/nephew. [Correction after consultation likely to be even closer]
    Do you know who your parents are? I will email you since this looks pretty sensitive to me

  19. I still do not quite understand the whole XY thing with half siblings. I am adopted and have a half brother through our birth mother. We came up as a match on ancestry as close family/first cousins. No shock there, we already knew we were related. However, I have a possible half sibling on my birth fathers side who just sent her DNA in. I know my DNA matches up distantly to the family line but this will be the first possible close match I have with my paternal side. If I’m reading right, every father passes down the same X DNA to each of his daughters? So would our test be more conclusive since we are both female?

    • My sister did ancestry.com
      I just ordered mine to see what shows up.
      We know several people from my
      Moms side that were on the report and no one that we know ANYWHERE on my dads side of the family showed up on the results. However 5 people showed up as 1st cousins (not related to moms side) and we have no idea who they are! Does that mean that who we thought was her gayer is indeed NOT her father? .

      • Theresa –
        Do you know for sure that cousins on your dad’s side have tested? If so, then yes he is not the bio dad.

        Some cases like this turn out to be because the parents used a sperm donor. Your test will help clarify this when it comes in.

        Another possibility if you are not sure any paternal side cousins tested …Those first cousins can be some other relationships if your dad or his dad fathered other children. Look at this calculator

  20. Catherine,
    You understand it just fine and are reading correctly. If you share a father with another female, your X chromosomes will match for the entire length. Send me the kit numbers once she is tested and uploaded to GEDmatch if you have any doubts.

  21. Hi there,
    I was wondering, could a half-sibling ever be an organ donor to the other sibling? Could their genetics ever be that close?
    The reason I ask, I want to be as accurate as possible for my latest book, where a half-sibling is able to save her brother. If it’s not, I’ll have to go strictly to a fictional ending, but it would be so nice if it could work out.
    I’m glad I found your article today. It was exactly what I was looking for.

  22. Kitty – hello! Very interesting blog and discussion here. It has been most helpful. Based on what I see here and on various other sites, my brother and I seem to share a relatively high number of cMs – per GEDmatch we share 3,586.9 cMs on C1 – C22 (longest block is 281.5 on C1), plus we share 196.1 cMs on the X (which appears to be the full X- right?).

    Can you conclude anything interesting or helpful from this “abnormally” close match?

    Since we both seem to have inherited an identical X chromosome from our mother, can we conclude that we inherited the X chromosome she inherited from her father, rather than the X she inherited from her mother? We do have an X match to a cousin from my mother’s paternal line, so I’m guessing that is the case.

    Any other clues here that can help us in our genealogical research? Thanks tons for your help and insight!

    • Hi Joel –
      Please do a one to one image only compare. If it is solid green and blue like this image – http://slides.com/kittycooper/gedmatch-10#/14 – then you likely uploaded the same kit twice. Or you are identical twins. Or the lab where you tested mixed up your results so that you have the same kit twice.
      That amount of shared DNA means these kits are the same.

  23. Hi Kitty,

    This is my fathers dna and he was given up for adoption. By dna testing we were able to find the mother side and the dna below is show family on the father side. We are trying to see if they are half siblings, cousins etc.
    What can you tell? thank you for your help.

    Largest segment = 54.6 cM
    Total of segments > 7 cM = 234.2 cM
    8 matching segments
    Estimated number of generations to MRCA = 3.0

    • Laurie –
      That is a solid match, likely a 2nd cousin to your Dad (subtract one from that number of generations to get the likely cousin-ship), see http://isogg.org/wiki/Autosomal_DNA_statistics – (it could also be a first cousin twice removed or a few other relationships in that neighborhood).
      Contact them! Tell them the story. Also look if they have a tree posted anywhere. Then look at all their gg-grandparents. Does your Dad match others descended from any of them?
      DNAadoption.com has lots of helpful resources as does DNA detectives on facebook

  24. Kitty – I feel like such an idiot! You are exactly correct. Somehow when uploading my and my brother’s kits to GEDmatch originally, I must have mixed up the file names and uploaded my brother’s kit twice – DOH!

    With our newly uploaded correct kits, GEDmatch shows us sharing a more normal 2,792.7 cMs. It shows “Estimated number of generations to MRCA = 1.2” – shouldn’t this be “1.0”, since we’re full brothers?

    Our X chromosome match is now shown as two large segments of 53.5 cMs and 78.9 cMs, respectively, for a total of 132.4 cMs (so looks like we share approx. 67.5% of the total X chromosome). Are there any conclusions to be drawn from this X sharing level?

    As I mentioned previously, we do know of one certain X match with a second cousin (2x removed) and this second cousin is on my mother’s father’s line. My brother matches this second cousin for two X segments of 24.9 cMs and 20.8 cMs, respectively; and I match this second cousin for the same initial 24.9 cMs segment that my brother matches her, but also match her on a longer 44.7 cMs segment that “contains” (has same start location as) the 20.8 cMs segment my brother matches this cousin on. Any other clues hidden in the way my brother and I match this second cousin?

    Again, thanks so much for your help!


  25. 1.0 would be an exact 50% but most of us are not exact. I share 47% of my DNA with my brother and we are 1.2 also.

    Your X sharing looks normal. Your mother gave you each slightly different X since she recombined what she got from her parents. Sorry no special clues from the X you both share with your 2nd cousin but it may be useful for figuring our other DNA cousin matches.

    One thing about X is that many “sex linked” genes like male baldness, color blindness, and some more harmful ones are carried on the X. So if your mom’s Dad kept his hair you are about 50% to keep yours! See https://en.wikipedia.org/wiki/Sex_linkage

    I see my brother with the same little bald spot that my mother’s Dad had …

  26. Okay, thanks Kitty. Makes perfect sense now. Yes, my maternal grandfather kept all of his hair, and so far so have I, so that’s one plus!

  27. Hi Kitty,

    I have a quick question if you don’t mind. I have just got my dna tested with AncestryDNA. Basically I’m suspecting that my uncle is maybe my father and my dad is actually my uncle. My siblings and I share the same mother and supposedly the same father (but I am suspecting it’s actually my uncle my dad’s brother that is possibly my father) I’m thinking that if I had my sister tested should our X be identical if we share the same dad? if not should it just be segments of the X if my sister father and my father are brothers aka my uncle is actually my dad? Sorry I know this sounds really confusing it is to me too! 😀

  28. Hi Kitty,
    Please can you give me some advice. If two full siblings both share a segment with a first maternal cousin on the yellow segment, would the yellow segment be a maternal match for the sibblings? Also if one of the sibblings have a match to another person on the same yellow segment but this match doesn’t match the other sibling until the segment turns green. Would it be safe to assume this match is to the paternal side as this match doesn’t match the maternal first cousin over this segment?

  29. If two siblings share a segment with a maternal first cousin then it rates to be maternal if it is > 11cM else it might be false (is anyone else from that cousin/s family tested?) although that is unlikely.
    Your second assumption is also likely provided the shared segment is large enough. If it is less than 7cM then it is more likely to be a false match than a good one.

  30. Hi Kitty,
    Thank you very much for your reply. 🙂
    The segments are larger than 11cm.
    Just out of curiosity do you think that endogamy in the population could affect this in this particular situation?

  31. Yes endogamy can affect this. Run the “are your parents related” on all these kits. Although that may not uncover this issue. For example if your maternal first cousin is distantly related to your paternal side, part of the matching segment could possibly come from your paternal side. Unlikely but possible particularly in an endogamous group. If your parents are tested you can use your maternal and paternal phased kit for comparisons. Otherwise go with the assumption you have, but keep comparing to other close relatives.

  32. Dear Kitty,

    My sisters and I have been trying to figure out which share paternal or maternal or both and it has gotten very confusing. My sisters share 194.1 on the X chromosome with each other. I share approximately 117 with each on the X chromosome. My daughter does not shar any X chromosome with either of them. In order to get 14cm with either I had to lower the threshold to about 200 at 2cm. Can you help me understand these relationships? Also, my sisters are supposed to have different fathers. And one more strange part although they share 194 on the X chromosome it says the largest segment is 128.

  33. Hi Kitty again,

    I think I need to give you even more explanations. On the X chromosome one to one match my sisters have a solid blue line all the way across sharing 196.1. The bar above the blue line is yellow. However the X chromosome matrix puts them a little lower at 194.4

    They are supposed to be half sisters to each other and to me. However on the X chromosome I share 117 cm with one and 118 cm with the other and my daughter does not share any part of the X chromosome with either of them. I look forward to learning how we are all related! Thank you!

  34. Gina –
    We use the X to determine which side, paternal or maternal, once we know people are half siblings from looking at the picture of the other chromosomes and the total cM. So look at the image of the other chromosomes when you compare the two of them for the tell tale green bars that indicate full siblings. Also what is the total cM?
    From the X, you appear to be a half sister to them and they appear to have received the same X as each other from their mother, unusual but possible.

  35. Ok- Thanks when you ask for total do you mean autosomal or XDNA

    Sister M- Autosomnal I am 1699.1 total with a 100.4 largest cM t. On X we are 117.8 total cm and 117.8 largest cm

    Sister D- Autosomnal I am 1498.8 total cM with a largest cM72.7. On the X we are 117.9 total cM and 117.9 largest.

    Can you explain why my daughter does not match either on the X chromosome?

    My daughter believes my sisters and I share don’t share the same mother but perhaps our mothers are related.

    Thanks again!

    • Gina –
      It is perfectly possible for your daughter to share no X with her half aunts when you share a mother with them. That would happen if you passed her your father’s X over that 117cM area where you share X with those half sisters.

      The total cM of autosomal is the most reliable predictor for close family BUT half siblings share the same amount of DNA as full aunts or grandparents, 25% or about 1700 cM autsomal. Both your presumed half sisters are a fit.So how much autosomal do they share with each other? Could they be full sisters? Or half sisters sharing a Dad (since they have a full X match)

      Where did you test? The mitochondrial DNA haplogroup will be the same for all of you if you have the same mother. 23andme provides that. The SNPs are tested in the ancestry data but you have to upload it elsewhere to get that information

      • Hello I am a bit confused me and a friend could have children that may share a father we have done a half sibling verse non related with a inconclusive result at the LR in favour vr half non related being 1 and probability percent in favour of half sibling vr non related being at 44.11% I NO the test is inconclusive but is there a chance they are half siblings? We did not provide swobs

        • Carly –
          My expertise is with the personal genome tests like from ancestry, 23andme or familytreeDNA. See http://blog.kittycooper.com/dna-basics/dna-testing/

          To answer your question, if the two children are tested at 23andme then one can tell conclusively when they are full siblings. Half siblings will look like aunt/niece or double first cousins. If one of the other testing companies is used then the results would have to be also loaded to gedmatch.com to figure it out.

  36. Could you please help, my son did a DNA test, behind my husbands back, with someone who came on the Internet to say she could be his half sister,
    the result came back 95/5% she also said my husbands brother could be her father, is this percentage high and clear proof.

  37. Hello, would people sharing this DNA definitely be half siblings? Is it possible for these people to be fun siblings? Here is the DNA they share.
    Largest segment = 104.8 cM
    Total of segments > 7 cM = 2,076.6 cM
    50 matching segments

    Thank You

  38. I was adopted I did the 23 and me and also just uploaded to Ged website ..There is one person that comes up on both sites ..it says we share 9 segments …500snps….total cm 2232and cm7.0 and 57.5 largest and MT) T2..And of course I’m lost with all this .Can someone help me …Thank you

    • Annette
      What is the total cm – 223.2 or 2232? I recommend you read everything you can. It takes a while to understand the significance of these matches and the various numbers. Go to DNAadoption.com and read their materials.
      Look at the charts here
      I will email you and have a quick look

  39. Quite a few of the posts right above are what I am currently dealing with. I love your comment that the DNA doesn’t lie. I uploaded my info to GEDMatch from Ancestry.com. Two other people that I had never met, but had shown a connection with on Ancestry, did the same thing. I would love to give you more details via email and ask your opinion if you get the chance (even though I am fairly certain I now know the truth and I am OK with it!:). I will be looking for the book Stranger in My Genes, for sure! Love this blog. So happy I found it. Thank you!!!

    • TK –
      if you have uploaded to GEDmatch, I am happy to take a quick look. Otherwise I just do not have the time to do this for free. I will email you.

  40. Ms. Kitty,
    Me and a gentlemen who I’ve always thought was my full brother took the ancestry DNA test. I uploaded the results to GEDMatch and we only share 1663.3 cMs. There were a few high numbers like 119, and a few 90’s in some areas but in your opinion is he my half brother and is it even possible that he could be my full brother?

    • Sounds like you are half siblings, sorry, but he is still your brother

      Look at the graphic comparison at GEDmatch. Half siblings will have no big green bars as in the 2nd image above. The first image is full siblings with the green bars

      • Thanks Ms. Kitty,

        I checked again and there are about 3 or 4 small green spots that are as big the 2nd largest green area in your Chr 2 posted for your full sibling. I was trying not to believe it but I guess its true. Thanks so much for your help!!

  41. That 1136 cM is most likely a first cousin or a half nephew. What is your age difference?

    Yes his mother’s father’s side is where it will be from the lack of other matches. You could be his mother’s half sibling on her father’s side for example. I take it she has not tested or is not available?

    So try and get relatives on his mother’s father’s side to test. Does his mother have any siblings? Do they have descendants, etc

  42. If I were to post results of a dna test for half-siblingship, could you tell me what the probability is? It says 98.7% and I don’t see how that is possible since we only are looking for half siblingship. Please help. Im “dna comparison” illiterate lol.

    • Probably not, my expertise is with autosomal tests from companies like ancestry.com or 23andme or FTDNA not with tests for specific relationships

  43. Hi Kitty,

    We just got the results from my Mom’s and her Sister’s DNA test at FTDNA. We are trying to confirm whether they are full sisters, half, or cousins. The results came back with a match of 2,445 cM, X match at 195 cM, longest block 137. They said possibly Full siblings, Half siblings, Grandparent/grandchild. Would it be possible for you to look at the chromosome browser and tell if they are indeed full sisters? Thank you!

  44. I’m trying to figure out if my half sister’s father (we have the same mother) is my fathers half brother or not. The question of who her father is has been debated in whispers for a long time This along with the fact that she has about 3-4% more Native American than I do and, as far as my knowledge goes, our mother and my father as well as his half brother are the only ones with native in them, makes me wonder what our DNA is telling us.
    We both did the Ancestry DNA test and it matched us as cousins. I uploaded both to GEDMATCH and we share 59 segments and 2064.2 cM with our highest numbers being 93.3, 90.5 and 70.1.
    Would this show us as “sister cousins” or as half siblings?

  45. The green bars, if they are large, suggest that either you are full siblings or that your fathers are related. I will email you.

  46. I believe I was scammed. I submitted my follicles for a DNA test. It took almost a month. I think the viability issues arise there. I was told I have a daughter. I believe the mother may have submitted the daughter half-brothers DNA. Could this come up as a match?

    • My expertise is with autosomal DNA tests not anything involving a follicle? If you and the daughter tested at Ancestry.com, familytreeDNA, MyHeritage, or 23andme the results would be clear. DNA does not lie. Otherwise I cannot help. For all those tests, the sex of the testee is clearly indicated by whether there is an XY or an XX.

  47. Jim without knowing where the test was done I cannot give you an answer. If this was an autosomal DNA test then the amount of DNA for parent child is unmistakable and a half sibling would share way less DNA. Autosomal tests like Ancestry use about 700,000 markers so are far more accurate than drugstore paternity tests

    • Ok, I think you answered my question. There is no way a half-sibling could be mistaken for a parent. I appreciate your answer though I was hoping for another.

      It has been a long ordeal since 2012. Finding out on Father’s Day about a 12 yo child. Then finding out she was given up for adoption. Then finding her. Then drama and no contact for 2 years. Then more drama…

      I keep trying because its the right thing to do because of the DNA test. I was hoping to be released on the possibility there was DNA fraud. But I guess not.

      Ill have to wait a few more years to see if she is ready.

      Thank you again.

  48. Hi kitty,
    I’ve been reading everything on your blog for over a month, but not sure I understand…. my uncle was rumored to have a different father, he shows relation to me as 1st cousin 902 cms & 43 dna segments
    So I had his sister tested and relatons to me is 1st-2nd cousins 852 cms across 40 dna segments so my Aunt has a different father as well?
    Do I understand this right?

    • It sounds like each child had a different Dad. The 1600 some cMs is half siblings and your numbers are half niece.
      Perhaps your grandmother’s husband was infertile so she used donors …

  49. What would be the expected cM shared between half siblings if: Brother B and sister S have child A and then Sister S and Father F have a child C. What would the expected shared cM be for Child A and Child C?

  50. 1080/43 Is it at all possible that this could be a half sibling? It is definitely not an aunt/niece match . Ancestry has said first cousin but when I called them they said they can not distinguish between a first cousin or a half sibling. Is there any way this could be a half sib or is it def too low.

  51. The girl that matched 1080/43 would either be a first cousin as her father would be my fathers brother. The other possibility as that we share the same father but different mother. There are basically two brothers involved and I am adopted.

  52. f.,

    Using Ancestry DNA testing, is it possible for a half-sibling and/or half-niece to appear as a 3rd-4th cousin instead of a sibling—given the explanations you have given under this topic concerning full- vs. half-siblings? Thanks!

  53. Hello!

    I supposedly share the same father as a newly discovered sister. We both did a 23 and me test and it said there was no overlapping DNA matches. Is it possible 23 and me got it wrong? I have adoption paperwork and a parental rights termination record with her father’s name listed as my biological father. We even look similar.


    • Luke –
      Something is wrong. Most likely he is not your Dad. Looking similar is not the final word. DNA does not lie.
      You could contact 23andme and ask if there is any possibility that there was a mix up in the lab, but that is unlikely.
      Best though would be to both retest at Ancestry or another company. Or perhaps just you retest, since you will probably want to search for your biological Dad. You can then compare your new test with hers at a third party site like GEDmatch.com

  54. One more question, I promise. Do you see a pattern with Ancestry DNA tests being off with their numbers. Is it possible they could be off by 200 cm? If they are lower than say 23 and me then I think it would be possible to be in the half sib range?

    • Fran, ancestry removes a small amount of matching Data that it considers “population” specific so that is possible but very unlikely to be so large. Please upload to GEDmatch and send me the two kit numbers via my contact form and I will look for you

  55. Kitty – I have another half vs. full sibling problem for you, if I may.

    According to GEDmatch, two sisters – one who tested at Ancestry and the other who tested at FTDNA – have an autosomal match of approximately 2900 cMs (longest block is 188 cMs), and have a full X-match at 196 cMs. However, the sisters have been told all their lives that they have different fathers – but that the two fathers were brothers. Is it possible, based on their DNA results that they could actually be “half” sisters, whose fathers were brothers, rather than full sisters who share the same father?

    When I saw the sisters’ results with the relatively high autosomal match of 2900 cMs and their full match on the entire X chromosome, I thought they absolutely had to be full sisters with the same father, notwithstanding what the sisters have been told. However, I’ve read recently that brothers can sometimes be identical X matches to each other (though I haven’t seen it yet).

    So, could these two sisters have received the exact same X chromosome but from different fathers, who were brothers, making the two sisters have a full X match (196 cMs)? Or, does the sisters’ “high” autosomal match of 2900 cMs, plus their full X match, mean the different fathers who were brothers scenario is really not possible?

    Oh, the fathers were NOT identical twins, but they were full brothers.

    Thanks for your help!

    • This certainly sounds like they are full sisters. I will email you for their kit numbers at GEDmatch but between the X and the high number of shared centimorgans, they are full sisters.

      Any chance the two brothers could test?

  56. Hello Kitty,

    My mom has a close family match on ancestry.com with whom she shares 1,659 CM and a first cousin match 872 Cm. My mom doesn’t know her biological father. What kind of match would show as a close family match?

  57. Hi kitty,

    I recently found a half sister on ancestry And uploaded the results on GEDmatch. The number seems very high though. Our shared centimorgans are 2,214 over 34 segments. Our largest shared segment is 182.8 then 146, 141, 131, 124, 114. There are many in the 70 to 90 range also. Does this seem like a normal possible range for half sisters?

    • Erin –
      That is high for a half sibling but almost within the range. I have seen other half siblings this high. If you come from a group that is at all endogamous, then these larger numbers are more likely.
      But look at the two images above. Do you have any of those green bars? If you have quite a few of them, then you are full siblings, otherwise with none or maybe one small one, you are halves. Of course the other possibility is that the parents (fathers?) you do not share are related!
      If you are still not sure, use my contact form to send me the two kit numbers but it may be a few days before I can look.

  58. I just got my results back and I’m having troubles understanding them is a 45% mean that me and the other one tested in the half sibling test half siblings ot none at all

  59. Does a 2344 cMs reading indicate full or half siblings? Seems to be on border line. Same mother just question about father.

    Thank You.

    • Jeff it could be either. Where are you tested? Ancestry removes population specific segments so it might be full siblings if tested there.

      More likely these are half siblings but compare them at GEDmatch and look for the green bars that indicate fully identical segments (FIRs). Full siblings will have quite a few of those.

      Also 23andme now shows those FIRs too.

  60. Both of us were tested by Ancestry.com DNA services. I live in Calif and my sibling in GA, However, we were both born in Pennsylvania but grew up in So. CA.

    • OK Jeff, you could be full siblings or half. You need to compare at GEDmatch in order to see which.
      Unless you each have close paternal and maternal relatives tested, then you can tell by whether they all match your sibling.

  61. “I have not been able to find this tool in the new 23andme experience, so I guess it is gone. If anyone finds it let me know.”

    I suppose you are aware that this feature is back now. But quirky.

    Back for a month or so. At first it only worked on your siblings. Now you can apply it to any pair of siblings or double cousins etc.

    It tells you how many Full (called Completely) Identical bars you have, but then the chromosome browser misses about half of them.

    Underneath is a very nice chart that is very accurate. And better than GedMatch since it includes the Start and Stop points for the Full/Completely Identical segments.

    • Yes I put an update in this post and I guess I need to blog about it sometime soon and wonderful that it shows the numbers!

      • Hi Kitty,
        Through ancestry I think I have found a possible half sister. We have both uploaded our DNA to gedmatch. We believe we share the same father. I’ve looked at your 1/2 sibling test and it seems similar but would like to have someone with experience to check. Can you help? Ps my father is deseased.

    • A 3/4 sib will have some FiRs but nowhere near as many as full sibs. The shared cMs will be around 2100. If you have such a case, send me the kit numbers via my contact form and I will give an opinion.

    • Sharon
      The children of double first cousins will look more like first cousins than the double 2nd cousins that they actually are

  62. MsKitty,

    I just entered the DNA kit numbers for my wife’s and her sister into GEDmatch. Up to a few moments ago we were positive that they were half siblings. The GEDmatch analysis listed on almost every chromosome matching FIRs, lots of green. We used Ancestry.com for the DNA raw data. Could there be the Ancestry.com data be giving a false reading or are they full siblings?

    • Sounds like they are full siblings after all! How many cMs?

      Send me the kit numbers and back story via my contact form and I will have a look later

  63. I just forwarded info (kit numbers etc) you requested on your contact form.

    Thank You


    FYI 2585 cMs over 60 dna segments

  64. We feel a little confused….. My husband did Ancestry DNA (he’s adopted, was looking for heritage, didn’t even know they gave matches!). He matched as close relative 1721cm’s over 51 segments with a woman. We can’t seem to pinpoint what the relationship is. (Not his birthmom) The second closest match is this woman’s half sibling (they have the same father), which the numbers to my husband are only 670cm over 20 segments. The high match seems to think my husband is her half sibling…wouldn’t the 3 of them have around the same #’s if they all had the same father?

  65. Lisa, that is very unusual. The numbers suggest that she is his aunt and her half brother is his half uncle.
    If they are all on gedmatch, send me the kit numbers via my contact form and I will look delicious more

  66. I found your blog while trying to find information on how to interpret my Ancestry DNA results. I have an estimated “first cousin” match that shares 1300 centimorgans across 47 segments. Our trees don’t match at all. Everyone tells me that that’s a rather high match for first cousins. I was wondering if it points more toward half-siblings? The match is only one year younger than I am, and I cannot see how he could be an uncle or nephew. There’s no way he could be my grandparent or vice versa. I feel completely blown away by the results I got. We also share a “2nd cousin” match (243cm across 11 segments). Half of my family tree no longer makes sense, and my heritage wasn’t at all what I thought it would be. Could someone help me make sense of this? I haven’t been able to get any responses when trying to message them.

  67. Amber –
    I am so sorry for your shock. This happens more than you would expect. Your parents are still your parents even if one of them is not biologically so.
    Or perhaps your half sibling (if he is) is the one to be surprised.

    Please join DNA detectives on Facebook and ask for help and/or the mailing list for DNAadoption.com on Yahoo.
    I will email you privately

  68. Kitty

    I have a question regarding 1/2 sib. and 1/2 aunt/uncle match.

    Seems most of these post here share a lot of DNA for their 1/2 sib matches… makes me wonder if I am on the right track or not. Both my mom and dad were adopted children and I recently got a new match on ancestry DNA and the match to my mom says close family-1st cousin (Predicted relationship: Close Family
    Possible range: Close family – 1st cousins
    Amount of Shared DNA
    1,351 centimorgans shared across 38 DNA segments)
    and same person to me says
    (Predicted relationship: 1st Cousins
    Possible range: 1st – 2nd cousins
    Amount of Shared DNA
    809 centimorgans shared across 30 DNA segments)

    Is it possible that this person would be my mom’s 1/2 sibling and my 1/2 aunt with these numbers? This persons DNA is not on gedmatch.

    On a separate note: Gedmatch shows a tie between on of your tests, my mom and me: (one to one with my mom)
    Largest segment = 34.4 cM
    Total of segments > 7 cM = 134.6 cM
    7 matching segments
    Estimated number of generations to MRCA = 3.4

  69. Just found a match to my adopted husband on ancestry.com (578 cM across 26 segments). Pretty sure its 1C1R on his dad’s side. I had already narrowed his bio dad down to the baby this match’s sister put up for adoption in the 1930s. He found them not too long ago. But they won’t tell me his name for personal reasons. I understand why.

    Anyway, no question here. Just wanted to say thanks for answering people’s questions.

  70. Hi Kitty
    My sister showed up as a half sister on 23& me same mother. Her chromosome diagram shows one bar and one color so our fathers don’t match. The one X chromosome bar is colored 2/3rds of the way across . Some of my relative matches match the uncolored end only and don’t show being related to her. Some matches also show on the uncolored portion of her bar only But seem related to her according to 23 and me. Are the ppl on the uncolored part of the x my dads side? And what about the others who match ?

  71. Hi Kitty,
    My siblings and I just got a very close DNA match we a lady at ancestry. I uploaded our Raw Scores to Gedmatch.
    My sister shares 981.7cM 18 matching segments Largest 138.1 CM 1.9MRCA
    My brother 662cM 17 segments largest segment 142.7cM 2.2MRCA
    Me 757cM 24 matching segments largest 146.7cM 2.1MRCA
    We share no XDNA. I have never had a match like this where I cou;d not figure the relation was.

    Is this a half sibling 1st or 2nd cousin?


    • Hi Anthony,
      That is not enough DNA for a half sibling. It is the right amount for a first cousin BUT the lack of X and the large chunks make me suspect something else … a half niece … in other words if you all have a half brother, son of your dad, the daughter of that half brother would share no X and have large chunks like this. Is that a possibility?

  72. Hi Kitty,
    Thanks for the response. I contacted my cousin Pam and she advised me that my youngest (now deceased) half uncle did have a son apparently he is estranged. I never met him. I guess he could be the father. It certainly is not Pam or her siblings based on DNA. I included their DNA with this lady.

    Largest segment 37.5cM 4 matching segments Total 89.2cM 3.7 MRCA
    Largest segment 44.3cM 12 matching segments Total 270.1 cM 2.9 MRCA
    Largest Segment 44.3 10 matching segments Total 196.5cM 3.1MRCA
    Largest segment 44.3 7 matching segments Total 127.9cM 3.4 MRCA

    What confuses me is why the disparity in the MRCA between my siblings and my half first cousins as well as the amount of DNA shared.

    I did not recognize any of the 61 names in her tree. It’s a touchy subject as perhaps the man she considers her birth father is not so. BTW my sister is the youngest at 65. Pam is also 65 her siblings late 50s-60. I can only assume that my uncles son must be 60+. The lady list 40-49 as her age at ancestry. I put the ball in her court. I did not tell her I was looking into this other than what I already told her. I am sure she is worried about it. Let’s face it in life these things happen. Btw we are all mixed ancestry people
    her not as much as my siblings and cousins. I never told her that she is a direct descendant of King Edward 1st. I know that for a fact as she has a lot of my and my siblings matches. Under the circumstances I believe she has other things on her mind.

    Thanks again,


    • Anthony
      The most likely explanation is that your deceased half uncle is this lady’s father. The best way to confirm that is to find his son and get him to test.

      How are your half first cousins, Pam et al, related? Because yes they share much less. That is possible if their parent just got less of the DNA that the half uncle got and less of the DNA he passed on but still seems too little ..

      Best if you make a McGuire diagram to look at this more carefully and send it to me. I will email you.

      • Hi Kitty,
        Thanks the lady emailed last night and told me that the man on her birth certificate may not be her biological father as per her mother. I think all 3 of us came to the same conclusion. Btw I discovered that you are my 25th cousin on Geni. I suspect that we are much closer. Welcome to the family lol. Thanks for all your help.


  73. Hello,
    I am hoping you can help me confirm whether my brother is my full sibling or if he could be my half sibling/first cousin (same mother, dads are siblings), or half-sibling (same mother, with unrelated dads). I have been reading around but I am not sure.

    This is what I get on Ancestry:
    2,395 centimorgans shared across 78 DNA segments

    On GED Match:
    Largest segment = 158.6 cM (2nd: 122, 3rd: 112, 4th: 106)
    Total of segments > 7 cM = 2,512.0 cM
    52 matching segments
    Estimated number of generations to MRCA = 1.3

    The GEDmatch.Com Autosomal Comparison shows me 5 chromosomes with virtually no green, some with some green, and about 6 with bigger green segments.


    • Marie –
      You are almost surely full siblings. Else possibly 3/4 siblings. In other words, if you are not full siblings, a possibility is same mother and fathers are brothers. Could that be?
      I will email you for the GEDmatch numbers to look at

  74. Hi there Kitty

    I’ve recently compared my DNA with that of my father’s female Cousin on Gedmatch. What sort of DNA match should I be expecting with this comparison?

    This is the result i get.

    Largest segment = 32.7 cM
    Total of segments > 7 cM = 130.6 cM
    6 matching segments
    Estimated number of generations to MRCA = 3.4

    400867 SNPs used for this comparison.

    Is this realistic.

    What I am trying to determine is if the same man was likely the father of my Grand father and my fathers cousins Mother. The records around 1896-1905 when they were born are pretty fluffy at best.

    • I removed the kit numbers for privacy but yes this is a good match, 4 of the matching segments are > 20 cM and would usually be about a 2nd cousin once removed. Could also be a full 2nd cousin or third cousin.

      Get a few more cousins to test, but yes she is your cousin.

    • In other words, a second cousin is someone descended from the same great-grandparents and in your generation. Once removed would be if one of you is one more generation down the tree. From your description, she is a first cousin once removed which also fits that amount of DNA.

    • Maybe I still did not answer that question. The amount of shared DNA gets more and more variable once you are outside of your immediate family. If she is your Dad’s first cousin but is only a half first cousin because he is NOT her grandad that would fit these numbers also. See
      To confirm or disprove you need to find cousins descended from the great grandad in question’s parents and test them. There will be no match if he is not the guy but you need several to be sure at that genetic distance.

      • Thankyou very much for your help.

        Yes getting descendants from the the great granddad in question would be great but who is he is the question I’m trying to resolve. I suspect that it may forever rest. However you never know your luck, something may pop out of the wood work as more folks get tested.

        Cheers and thanks again.


        • Peter –
          Do you have a male line descendant of this mystery ancestor to test? In that case a Y DNA test to at least 37 markers may give you the surname and some further back relatives …

          Autosomal test as many cousins descended from him as will do it and keep track of the matches that have to be from his line … some day it will resolve …

  75. Earlier in the year, someone contacted me on Ancestry after having their DNA tested and came up as “close family/1st cousin” match. Our cM are at 1537 on Ancestry and 1598.8 on GedMatch, while our longest matching segment is at 142.6. Via many email discussions, we figured out we probably share the same father, but upon sharing this with my sister, she doesn’t believe me, nor does she trust Ancestry. Can you help me/possible half-brother on our quest and offer some valid proof that this is indeed possible?

  76. Hello Kitty
    You are always so helpful and I hope you can answer this query for me. after over 70 years of my brother and I believing we were half-siblings, DNA results showed we were full brother and sister. As I never knew who my father was, we assumed that his father must also have been mine. A first cousin once removed from my brother’s paternal family agreed to DNA test. the results are back and there is no match to either my brother or myself. I did a ‘one to one’ comparison on GEDmatch and there were no matching segments.
    What are the chances that the cousin inherited totally different Chromosomes from us?
    Thank you for your time and a great site.


    • Sorry, there is no chance you would not match a first cousin once removed. Could that cousin have misattributed parentage? If so try another one … Else go look at the methodology at DNAadoption for finding an unknown parent to find your biological dad

      • Hello Kitty
        You are always so helpful and I hope you can answer this query for me. after over 70 years of my brother and I believing we were half-siblings, DNA results showed we were full brother and sister. As I never knew who my father was, we assumed that his father must also have been mine. A first cousin once removed from my brother’s paternal family agreed to DNA test. the results are back and there is no match to either my brother or myself. I did a ‘one to one’ comparison on GEDmatch and there were no matching segments.
        What are the chances that the cousin inherited totally different Chromosomes from us?
        Thank you for your time and a great site.


        Thank you Kitty. I think the cousin’s parentage is correct. I have seen their DNA matches to their family, and my brother and I do not have any of them on our matches either, so I think it is fairly conclusive. I know we are not adopted, but I will follow your advice.

        Again, many thanks.


  77. ISOGG says that shared centimorgans (as you mention as well) equal 2550 for full siblings. So if the shared centimorgans are 2543 is that close enough to consider full siblings? I am really just trying to make absolutely sure.


  78. Thanks Kitty, I was 98% confident. It is that 2% that will plague a person sometimes, lol!

    I appreciate the response and the reassurance!

  79. Kitty, I’m an adoptee. I’m aware of my maternal line, but seeking paternal lineage. On ancestry site, I discovered 2 close family/1st cousin matches. I believe both are half siblings. With the female, I share 1569 cms. With the male I share 1357cm (the male uploaded his data to gedmatch, which changed the relationship of cms to 1441). I was really wondering whether the male and I (sharing the 1357cms) were instead a lesser relationship than half-siblings until I discovered the he and the female actually share 2100cm together. Am I correct to assume that this would make the 3 of us half-siblings? All 3 of us are searching for an unknown birthfather. Also, is there a reason that my half-brother and half sister share such a high cm (2100) between them, and the number I share with each is 1569 & 1357 (so much lesser)? Pretty confused with this.

  80. Kitty, I’ve been unable to get my half sister to do much more than her initial Ancestry test kit. After she discovered that the father who raised her was not her bio-dad, she has pretty much stopped. Says she’s glad to have discovered that she has a half-sister (me) and half brother, but doesn’t feel the need to do more. In regard to my half brother, Gedmatch shows our largest seg shared is 129.5cm, total segs 1437 cm, with 33 matching segs. It seems quite certain that he and my half sister are indeed siblings (2100 cm between them). They were both born within 30 minutes distance apart in the same area of the state in 1954, within 3 mos of each other. I was born 9 yrs later. I share 1569 cm with my presumed half sibling. It is safe to say though that we are all half siblings, correct?

  81. P.S. Neither of these matches have older brothers who could have been my dad, so we have ruled out either of them (even with the 9yr age difference) being my aunt and uncle.

    • Ally,
      Sounds like you know your stuff and have eliminated the other possibilities so yes your half siblings.

      How many matching segments > 100 cM does your half brother have?

  82. Thanks, Kitty. I’m trying to learn as much as I can. These matches (half sister and half brother) are pretty stunning. I’m trying to make certain as much as I can. I’m pretty confident with the 1569 cm match with my sister. Its my half-brother match with 1357(ancestry) , 1441(gedmatch) that I was questioning really. I checked the chromosones.. on 2 (113 segs), 4(116), 8(59), 9(68), 10(60), 17(96, 18(129). 21(60 segs)…. The others are values between 10 and 50 or so. The 22nd has no shared segs. What do you think? Can I with a reasonable confidence assume he is also my half-sibling? (he shares 2100 cm with my half sister match, with whom I share 1569 with).

  83. Kitty, another question… do you think that my half siblings share such a high cm (2100) with each other because they may have another common relative? Like maybe their moms are also related to each other. I do know for a certainty that my mom was not related to them. But both of them were conceived, born, and parents lived, within close vicinity of each other and within months of each other. What possible reasons would they share such a high cm relationship, when I only share around 1350 and 1550 with each of them?… if all the 3 of us have in common is the dad? That is what baffles me.

  84. Hello Kitty

    I contacted you recently because my brother and I are trying to find out who our father and paternal family are.

    We have both had a DNA match on Ancestry to a potential 3rd cousin. I understand that we will probably share a GGGrandparent. I have been able to trace 14 of this persons 16 GGGrandparents, and I have the GGrandparents of the missing pair. Obviously I only have 4 pairs of GGGrandparents on my mother’s side. None of my maternal GGGrandparents are the same as this potential cousins, and there are no recognisable surnames with his parents upwards. Does this mean that this cousin could be from my paternal family?

    If this is so, can you give me a guide of what to do next? I realise it could involve lots of research and time, but I’m not sure what my next move would be.

    Thank you so much for all your help, Kitty.


  85. Hi again Kitty

    I think this will be a bit too technical for me, but thank you for your reply.

    Am I right in thinking that this 3rd cousin is on my paternal family’s side, because my maternal GGGrandparents are different from all his GGGrandparents?



    • Pat –
      No you cannot draw that conclusion. Sometimes a 3rd cousin match is actually related twice so a double 6th cousin for example. These predicted DNA relationships are not a sure thing after close family.
      The way to tell that he is paternal is if he does not match any of the close cousins you have found on the maternal side

  86. Thank you, Kitty

    It really gets complicated doesn’t it. Unfortunately, my immediate maternal family is small – only one 1st cousin and a couple of second cousins. I wish I was better with figures and numbers to be able to use some of the tools available.

    I am not able to look at the shared matches with this predicted 3rd cousin on Ancestry. It does not seem to have this facility other than for my own account.

    Invaluable help as always, Kitty.


    • To look at shared matches, click on the View Match button for him on your page of matches. The next page which shows the details of your match with him includes a button called Shared Matches.
      You do not need a paid membership to see these but you do need one to see trees

      • Thank you, Kitty

        It really gets complicated doesn’t it. Unfortunately, my immediate maternal family is small – only one 1st cousin and a couple of second cousins. I wish I was better with figures and numbers to be able to use some of the tools available.

        I am not able to look at the shared matches with this predicted 3rd cousin on Ancestry. It does not seem to have this facility other than for my own account.

        Invaluable help as always, Kitty.


  87. Hello Kitty

    I m sorry, I misunderstood what you meant. I have looked at my 3rd cousin’s shared matches and they only have 2 – my brother and my son.

    I am a paid up member of Ancestry, so no problem there.

    As you know, I only recently found out my brother and I are full siblings. Would it help if he took a Y DNA test? Don’t know why it never crossed my mind before!

    Many thanks


  88. Hi MsKitty,
    Do you do any consults? I am trying to find out who my bio father was and in the process have discovered a half sister with whom I am in frequent contact. I have tested myself, my mother and 2 of my 5 sons and uploaded our raw data to Gedmatch as has my half sister. Neither of us has any idea who our bio dad could have been. Of course, he is now probably is log deceased as we are 61 and 74 years old. All I am hoping for is that I can build a family tree and gift this to my children and grandchildren as the other half their family.
    If you are willing and able, please could you let me know approximate cost for this.
    thank you for your wonderful blogs

    • Jane
      How exciting that you found a half sister! With her and your mother tested it is very likely we can find your father’s family provided any of his cousins have tested. Are you tested at ancestry? They have the largest database.
      I will email you

  89. Dear confused,
    Take a deep breath. Family is family regardless of how much shared genetic material there is.
    The ISOGG wiki always has the latest numbers for the cMs of various relationships or go to Blaine Bettinger’s blog
    but please remember these are a range. Always best to compare at GEDmatch as you have.
    However you can perhaps determine if your mother’s father is biological by looking for matches on his line. Build a good tree and see what ancestry finds for you. See

    • Yes that is likely with such a large piece of X but X can last a long time, so if his mother is distantly related to you then he could still be a half sib with a shared dad … I will email you

  90. Dear Ms. Kitty,

    I am an administrator of several DNA projects at FTDNA. But this is a personal question.

    I know through Y-DNA and atDNA who my pair of biological great-grandparents are on my father’s paternal side. However, I am trying to determine which of their 2 sons is my biological grandfather. One of the sons has a son and I just tested both his Y-DNA and atDNA. The Y-DNA is spot on (which I knew it would be. Was just confirming through DNA). I was hoping the atDNA would 100% confirm whether this man and my father are are half -siblings or first cousins. The number of total cM they share is 957. This puts them in range for both possible relationships. However, when I compare their chromosomes on the Chromosome Browser, they DO NOT share DNA on all 22 chromosomes. They only share DNA on 17 out of the 22 chromosomes. I have a pair of half-sisters in one of my projects and they share DNA on all 22 chromosomes. So…does the fact that my dad and his new relative don’t share DNA on all 22 chromosomes mean they are first cousins? Or could they still be half-brothers?

    Thanks for any light you can shed on this!

    • It is OK for half siblings to not share DNA on every chromosome however the total number of cM is low for half siblings. How large are the largest three segments? If they are not all over 100cM then they are not paternal half sibs

  91. Hi there. I have a question regarding my mother and her sister’s DNA. My mother has always questioned whether or not her and her siblings have the same father? They just recently did their DNA kits at MyHeritage and received their results. We are a little confused on the results and I am hoping you can help me clarify the results. I assumed that if they indeed had the same mother and father, they would share 50% DNA. However, the results are a little confusing because it shows that they have 31.7% (2,300.1 cM) shared DNA. Would this make them half siblings? Their largest segment is 167.6 cM and they have 42 shared segments. I would so much appreciate if you could maybe give us a little insight and understanding on these results. Thanks in advance!

    • Crystal,
      They could be either stil, more likely full siblings but if you upload to GEDmatch you can look at the one to one comparison picture and know for sure. Full siblings will have many green bars for fully identical segments as in the article above

  92. Hi,
    so the easy thing to understand is that this is all very complicated. I’m hoping you can give me somewhat of a simple answer here to my dilemma. I’m trying to determine which of two men is my biological father. the first man is dead, but if he is my father then I would have 1 full brother, 1 half brother, and 2 half sisters. the second man for all intents is just as unreachable. My question is, should I ask my potential full brother or the other brother, who is potentially unrelated to me if this man is not my father? I WILL be able to get a sample from my mother. I don’t need anything to be court acceptable, i simply want to know if the dead man is my biological father. So, to say it another way, man A has 2 sons, one of them shares a mother with me. which son gives me a better answer to know if man A is my father?

  93. Anna –
    Either one is fine, but the full brother will be absolutely unmistakable in the DNA whereas the other can rarely look like a first cousin … however the half brother would be useful for figuring out which matches are paternal …

    Can’t you test both? For your purpose the full is better

    • My full brother lives over a thousand miles away and wont answer phone calls most of the time so he is unreliable. The half brother will be visiting me in a few weeks and will actually cooperate. I’m curious as to how the half brother could look like a cousin. If man A, who is his father, is not my father, that would mean we are not siblings at all. is there a certain kind of test I should be looking at, I know there were a couple different ones mentioned. Would we all have to be tested at the same time? Or could I do the testing with the brother i do not share a mother with and then if possible compare later test results from the full brother? Lastly, is having my mother tested helpful only if her son(full brother, unreliable one) is tested?

  94. Anna –
    Your half brother’s test is fine. In your case there will be almost no matching DNA if his Dad is not your Dad.
    To answer your other question, there is some overlap between a first cousin and a half sibling in the amount of DNA shared. A high first cousin and a low half sib will share similar amounts (in the low 1300s) but the half sib will share more large segments. See this chart

    • I am sorry I keep coming up with questions for you, this will be the last one, I hope! I just read through previous comments again, and saw something I missed about a semi similar situation. Would having this mans daughter, from a different mother, tested be even more conclusive then having his son tested? if she is my half sister, I would share an entire X line with her, correct? whereas my half brother would be less conclusive… is this right?

  95. Would you please recommend where/ what test I should get? I’m looking at 23 and me, the ancestry test. or the family finder test from family tree DNA. Thank you so much for all your help!

    • Wherever you test, you can upload to GEDmatch for more details. I really cannot make that decision for you, but in your situation perhaps 23andme
      23andme has the best chromosome browser comparison tools as they include FIRs and also show you a chromosome map of your ethnicity. however Ancestry has the largest database for finding cousins
      Today is the last day of the sale at ancestry. 23andme may be on sale still via Amazon prime if you have that

    • Anna
      No it is not but Family Tree DNA also has very good tools they just do not include the FIRs. Tests results from the other companies can also be uploaded to Family Tree DNA

  96. Hi Kitty
    So with a half sibling, would the X dna on gedmatch show mostly “green” matches? Sorta the opposite of the other chromosomes.

    I wanted to confirm I was reading the graphs correctly.


  97. Hi,

    I am trying to determine if my Aunt and father are full siblings. I have a suspicion that while they share the same mother, my father’s father is my Aunt grandfather. IE My grandmother had a relationship with a a man and had his child (my dad), and then had a relationship with that man’s son and had my aunt.

    I have their DNA profiles on 23 & Me. They do not share any fully identical dna on chromosomes 19, 22 or X. Is this an indication that they are are half siblings? If not what would be the best way to determine this given the possibility that with this scenario, each of the fathers would share DNA?


  98. Hi Ms Kitty,

    I’m disappointed. I’m 40 and After shockingly discovering that my dad is not my bio-dad via AncestryDNA, I’ve since taken tests and uploaded my data on all the major platforms (MyHeritage, 23andMe, FTDNA and Gedmatch.com).

    On 23andMe, I got a close match (1st cousin prediction) to a young man (18 y/o) who was adopted and does not know his birth family. He put his results on gedmatch at my request, so from there I was able to compare his dna to my moms to confirm there isn’t a relation to my mother. So he has to be related through my bio-dad.

    On 23andMe it says we are a First Cousin, 15.2% shared, 31 segments.
    On Gedmatch, our Autosomal Total cM is 1080, largest cM 102.9, Gen 1.87.
    our x-dna is Total 62.5, Largest 62.5

    Is it possible that his mom is my half sister? I’m so confused. I have no support from my mother who claims that the 4 ancestry tests + the 1 paternity test from DDC is not valid because they were done through the mail.

    • Yes based on the age difference it is more likely that his mother is your half sister than you are first cousins.

      Give your mother some space, she is in denial

      Meanwhile you can find your birth Dad and help your presumed half nephew by using various proven techniques with your DNA test. Look at the resources listed on my adoption page

      And come back to my blog in a few days for my next post on this topic

  99. Hi Miss Kitty,

    I recently found out my dad isn’t my dad. I took a dna test on ancestry.com and just received a message from a gentleman in Australia that doesn’t know his birth parents and he and his twin were adopted. They don’t have any information on biological parents. I came up as his closest relation under extremely high confidence score to be CLOSE FAMILY-1st cousin. I’m assuming half-brother because of our 3 year age difference. I have a half brother (same mom/different dad) and he also did dna test on Ancestry. They are not a match! This means that this gentleman (and his twin) and I are related through our father…..whoever that may be.
    My question is half-siblings or uncle? Uploaded Raw DNA to GENMATCH and did One on One Comparison:
    Largest segment= 127.8 cM
    Total segments .7 cM=1570.8 cM
    34 matching segments

    Ancestry results- 1522 centimorgans shared across 48 dna segments.

    Please help me solve this puzzle! Is there another test to be certain of our relationship?

      • Thank you Miss Kitty…..we also show under CLOSE FAMILY in each others Ancestry results and share the same 3 relations (in same order) under the 2nd COUSIN heading. Would this also confirm we are half siblings?
        Thank you so much for your quick response!

  100. Can you help me understand what this means. This is a match that came up as a close relative-1st cousin on Ancestry. We uploaded our info to gedmatch.com

    Largest segment 83.7cM
    Total half match segments HIR)=1818.8 50.7%
    401159 SNPs used for this comparison
    58.6% SNPs are full identical.

    Is it possible to confirm if we are half siblings? Both adopted

    • Amy –
      I have not seen the line “58.6% SNPs are full identical” before – is this from Genesis? Fully identical segments only occur in full siblings, double first cousins, or other complicated double relationships.
      I will email you

  101. I was adopted at birth, so I did a test on Ancestry to try and locate my birth family. I found my bio mom, but she had passed away. So no info on birth father. I got a “1st cousin” match in May. I knew he had no relation to my bio mom’s family, so I figured it was my birth father’s side. I contacted my “1st cousin match” and he only has one Uncle, so I sent my potential bio dad a letter, explaining that I thought I was his biological child, etc. He had no idea I existed, but did confirm to have a one night thing with my birth mother. Things went very smoothly. We’ve spoken weekly, since. We were both ecstatic to have found one another. I asked him to test through Ancestry, just to be on the safe side, which he did, but we met last week, before the results were in, because we really thought there was no other possibilities. WRONG! We got the results the night before he left. We were both devastated. According to his results on Ancestry, we are a “Close Family” match, with 1823cms across 40 segments with a MRCA of 1.5 on GEDmatch. So, he is apparently my Uncle. So, back to the drawing board. I suspect my “1st cousin” is now my half brother. He shows on Ancestry to be a “1st cousin Match” with 1205 cms shared across 40 segments. On GED match it shows we are 1253.6 cms shared across 24 segments. Largest segment is 180.3cms. Other larger segments are 160.4, 98.4, and 87.5. With a MRCA of 1.8. My Uncle asked his brother, a few days ago, without any other info, if he was ever with my birth mom, and he said YES! They’re from a small town… So, based on these results, do you think my “1st cousin” is my half brother? My possible half bro is asking his dad to take a test, but he has some mental issues, so we’re not sure if he will. I’d just like to ease my mind a little. I’d appreciate any help! Thanks!

    • Although the total cMs are under the expected amount for a half brother, the number of segments and segment sizes fit. Such large segments are usually only seen in paternal half siblings. Still it would be best if your half brother talks your presumed dad into testing.

      As to your uncle who is not your dad, he is still part of your birth family, enjoy knowing him and your half brother.

    • I just wanted to follow up and let you know, my “1st cousin match”, from Ancestry, is in fact, my half brother. He had his dad test, and his dad is indeed my birth father. You were right! Thank you for all your help!

  102. Hi Miss Kitty,

    I have recently had DNA testing for my father, my aunt (his sister) and myself through myheritage. I am wondering if my father and my Aunt could be half siblings. They share 2,222.9cM, 30 shared segments of which the largest segment is 224.3cM. They have 30.7 percent shared DNA.

    I am doubting a full sibling relationship between them because their ethnicity report is so different. My father shows 72 percent English, 18 percent Scandinavian and 10 percent North and West European. My aunt shows 62 percent West European and 38 percent Scandinavian. No English.

    My report proves that he is my father with 50 percent shared DNA and my aunt and I share 20 percent (1,446.8 cM). It also shows me as 56.3 percent English, 36.8 percent North and West European and 6.1 percent Scandinavian. (My mother was also tested – 85.4 percent North and West European, 12.4 percent English and 2.2 percent Scandinavian).

    I have been doing my family tree for many years and both parents ancestors are through and through Dutch for many centuries. I am finding a small amount of shared surnames on my father’s parents side. Do you think that my father and aunt could be half siblings? To be honest, my father looks nothing like his father.

    Thank you in advance.

  103. Hi
    I did an Ancestry DNA test and so did two of my half sisters. They are also half sisters. So we all share the same dad but 3 different mums. I am a male in Australia they are in the US. There is is a lot of circumstantial evidence that we are half siblings but since the DNA test we are distraught that we don’t come up as matches. They come up as matches but I don’t show up.
    Does this conclusively mean I am not their half sibling?

  104. Hello! My sister matched 2207 centimorgans across 69 DNA segments and believes our father to be her father. Our distant cousin matched this same lady at 1516 centimorgans and believe they have the same mother! Could this be conclusive, both my father and cousin’s mother are deceased. My father and cousin’s mother were 1st cousin’s as their fathers were brothers. Thank you!

  105. I have daughters who are fraternal twins. Their shared cMs seems very high given what I had read about averages and ranges. They have 2932 HID cMs over 39 segments and 1114 FID cMs over 31 segments. If I add them together they end up with 4046 shared cMs.

    I ran a match on two of my relatives who are siblings as well and their numbers are 4016.

    Are these just unusually strong matches?

  106. Hi Kitty,
    If I could pick your brain?
    A match shows for me and my 1/2 aunt. She is 1-2 cousin to aunt and 2-3 for me. The odd thing is she shares 74.3 cms on x chromosome, largest cm is 66.8 and 5,727 snps
    Her total cms to aunt is 383.1 cms largest cm 38.7
    Me and my aunt only share 32.2 cms on x chromosome 4,358 snps
    This match and I total cms is 254.2 and x match at 22 cms
    I believe I have confirmed she is related to us through my gg grandmother
    But am I wrong in thinking she must be related another way also because of the numbers? We are both very interested in the connection as it was a complete suprise to her, not to me as my g grandmother was adopted so used to lots of mystery. Can you offer any insight?
    Kindest regards

  107. The X has an unusual inheritance path and you can share quite large segments with a distant cousin so do not worry about that part of the match.

    She could easily be a half first cousin to your aunt. In other words, one of her parents could be your mystery gg grandmother’s sibling. What is the age difference? Is that a possibility? This chart is a big help for visualizing the possible relationships

  108. I’m more confused than ever now, she’s only 34 and my aunt is 69
    She says her aunt who is in her 60’s had at least 1 child in her teens and had another 3 children she adopted out who are in their 30’s and 40’s now.
    No names in her family tree are familiar.
    My Aunt and I only tested to find out where in Africa my ancestors came from and found out her Mother had 3 children all different father’s, the 4th child most likely a different father as well. What a mess! I really admire how you keep all this straight and take the time to answer everyones questions!
    I’ll buy you a glass!

    • Sorry, perhaps I am the one confused. That is a fairly close relative, closer than your gg grand mother. Look at the possibilities on that calculator, 1st1R or 1st2R or 2nd to your aunt or her great niece …

      Could she be adopted and not know it? Or one of her parents? Or perhaps her Dad is not who she thought? The way to tell that is to test more relatives. Does she have any matches on her Dad’s side?

  109. Her Mom and Dad are the right age if my grandmother had another child she gave up, which is entirely possible! This match says it can’t be herself that was adopted, she thinks it’s not her parents either.
    I only have a niece and my aunts children (so 2nd cousins if she’s my half Aunt right?)
    Would they help solve this?
    What a mess! Lol

    • Is the niece from a different mom than the tested aunt? Sure

      But if your match can get a maternal and a paternal cousin to test that would help resolve this best

  110. Kitty-

    I had a potential half sister test and her results came back on Ancestry at only 1206 cms across 56 segments. That is a 1st cousin typically, however it is impossible for her to be my 1st cousin. She cannot be my niece or other similar numbered options. She did just have a baby (I read about microchimerism changing DNA). Could she still be my half sister? I see no other options.

    • CEH –
      Ancestry removes some matching DNA it considers population specific so if you both upload your results to GEDmatch or familytreeDna and compare there you will likely share more and the numbers will fall into the low end of half siblings.
      If you share a Dad, you will share a full X chromosome. if you share a mom, your mtDNA will match. You can get the latter from James Lick’s tools or promethease.

  111. We’re trying to find info on my FIL’s parentage and on ancestry, we found a woman with 1658 Cm and 68 segments in common. I was guessing this would be a half sibling but looking into the family tree, there’s a possibility that she could be a double cousin. Do you know what we could look for in the dna in order to figure this out? Thanks!

  112. Hello Kitty,

    I love you blog, thank you!!

    Do the below GedMatch results look like 1st cousin or 1/2 sib? I am a 40 year old male and these results are with a 49 year old male. We do know we have different mothers. 🙂

    Largest segment = 191.2 cM
    Total of segments > 7 cM = 1,480.5 cM
    24 matching segments
    Estimated number of generations to MRCA = 1.6

    Thank you in advance,

  113. Thank you for your response and advice.

    Tested at AncestryDNA. Don’t know our haplogroups but will go to promethease.

    Thanks so much. I’ll report back with results.

  114. I have 3 brothers that match each other as full siblings but I show up as half sibling to all 3. This is a shock. Is it possible that I could be a full sibling and the test are not correct. Any suggestion on how to be for sure of our results?

    • Shar,
      Sorry, it is very likely correct. You need to upload your results and one brother to GEDmatch unless you are all tested at 23andme. The reason is to be sure there are no fully identical regions (FIRs) as described above.
      Full siblings will always share many FIRs. So if you have those, you would be full siblings after all

  115. Hi Kitty,
    My husband and his brother are not sure whether they are full or half siblings. What company and what test do you recommend to give them a clear and difinitive answer? Thank you for your help.

    • 23andme shows the fully identical regions that distinguish full siblings. But the other companies tests can be uploaded to Gedmatch.com to get those as well. So whichever you prefer.

  116. Hello-
    I can see this is an ongoing hot topic, one I find myself working on with my mother. I recently found a FTDNA match at 1625 cm,45 shared segments with longest segments being 140, 131, 115, 104.
    X is not full match, it has 2 segments of 89.34 and 96.8.
    With some digging I discovered their mothers are first cousins. But 1625 is too much shared for her and her match to be only second cousins.
    Are 1625 cm too low for them to share a father?
    Or maybe Fathers were brothers?
    I have reached out to the match just mentioning the close connection but have not heard back. My mom is uploaded to Gedmatch but the other person is not.
    Any thoughts?

  117. That amount of shared DNA and those large segment sizes suggest a shared Dad but if there is also a first cousin relationship on the mother’s side, that should increase the amount of shared DNA. Still this is quite possible. Also the second relationshp could add FIRs (fully identical regions) which do not get counted in the total. It would be interesting to see this comparison at GEDmatch which shows FIRs. Email me if you upload there.

  118. Hello Kitty

    We were in contact a couple of months ago, and I took the advice you gave me and bought my brother a YDNA kit with FTDNA. We have now had the results back. (Just to recap we recently found from DNA testing that we are full siblings, and are now looking for our paternal family).
    What surprised us most was that he had 58 matches, and almost all
    of them had different surnames. None of them were familiar. He had three matches with a genetic difference of 2. Two of these had the same surname (family A). There were also five matches with the “family A” surname with a genetic difference of 3.

    The other match with the genetic difference of 2 (family B) has a surname we know from step-family members.

    I contacted “family A” and they are really only concerned with relatives with the same surname, which, of course, my brother and I do not know. However, “family B” in the USA, apparently originated from the same part of England, in the 1700s, where I was born.

    Are you able to tell us why there are so many different matches, and why we have two different families with the same related matches?

    Thank you.

    • Pat –
      Y matches of 4 steps or more are often before surnames were taken and there can be many of them.
      However it sounds like the surname is the one for family A, the single B person can have an NPE or adoption on their line. So run with it …

      • Thank you Kitty I wil.

        Since my last message, I have been looking into family B. I have a possible maternal half-niece. If she took a DNA test would it show if her father (deceased), was really my full sibling?

        Thanks again and best wishes for the coming festive season.


          • Hello Kitty

            Re: Finding my father/paternal family.

            The DNA results for my niece (half niece) are back, and like you say there is overlap. I have looked on the DNA Painter chart as you suggested, but am more confused.

            FTDNA RESULTS
            My result: 1482 Cms. Longest block 122. AUNT
            My full brother: 1364 Cms. Longest block 124. UNCLE
            My son: 651 Cms. Longest block 60. I COUSIN

            DNA Painter shows me as her Aunt
            My brother as either Uncle/Half Uncle
            My son as Half 1 Cousin/1 Cousin
            My brother’s results seem to be in the Half Uncle perimeter and my son’s favour the Half 1cousin.

            We have always believed that my niece’s father (deceased) was our half-brother, so I know you will understand why we need to be sure. Is my own result a definite?

            Going by my full brother’s Y results, is it possible that our father could be my niece’s uncle (our ‘half’ brother’s brother)?

            Thank you for your time and excellent advice as always.


          • Sorry Kitty

            Red my last post – I meant could our father be my neice’s Great Uncle (my ‘half’ brother’s Uncle)

            Regards Pat

          • Now I am confused. The numbers are consistant with her being your full or half niece but not a half great niece
            if she is maternal side, and her dad a maternal half brother then these should be some X sharing too. How much?
            If you are using numbers from family tree DNA you need to export the shared segment sizes to a spreadsheet and then total up ONLY the ones 7cM and higher.
            Try making a diagram like this
            It often makes it cleare

  119. Hi- recently I did my ancestry DNA. A few weeks ago someone that I have no idea the relation popped up as having 1875 centimorgans across 68 strands of DNA. I am assuming this person is my half sister on my paternal side but she is not responding to me so I have no other way of knowing. Is this a possibility? She cannot possibly be an aunt, grandparent or first cousin. My second cousin’s all show up at 500 and under centimorgans. Thank you for your time, I appreciate it.

  120. Hi Kitty,
    I recently had sibling DNA testing done with two sisters to determine if we were half or full sibs. I find the wording of each conclusion confusing. Can you help me understand what these mean, please?
    Conclusion Sib 1:
    “With regards to the question of whether these two individuals are full or half siblings, they are 2553 times more likely to be half siblings with a probability of 99.96%. With regards to the question of whether they are half siblings or unrelated, they are 180733 times more likely to be half siblings with a probability of 99.99%.”
    Full/Half Sibling Likelihood: <1
    Probability: 0.03%
    Half/Unrelated Likelihood: 180733
    Probability: 99.99%

    Conclusion Sib 2:
    "With regards to the question of whether these two individuals are full or half siblings, they are 6 times more likely to be half siblings with a probability of 86.67%. With regards to the question of whether they are half siblings or unrelated, they are 628432089 times more likely to be half siblings with a probability of 99.99%.
    Full/Half Sibling Likelihood: <1
    Probability: 13.32%
    Half/Unrelated Likelihood: 628432089
    Probability: 99.99%

    It seems to me that according to the above, I may be full sibling to Sib 1 and half sibling to Sib 2. Am I correct?

    • This is not my area of expertise but it sounds like they are both half siblings to me. Call customer support at the company you used.
      Better to test with 23andme to answer this question or ancestryDNA and upload results to gedmatch

  121. Hi Kitty,

    My Dad and I did the Ancestry DNA testing and got a match that showed up in their range of close family to first cousin. We had no idea who this person was but I was finally able to make contact with his family and we are trying to confirm the relationship. We know the match is related on my paternal grandfather’s side due to other shared matches, but are not sure if he is a half brother to my father or a half brother to my grandfather.

    I’ve loaded all of our info into GEDmatch and these are the results to the one-to-one compare are as follows:

    Largest segment = 141.4 cM
    Total of segments > 7 cM = 1,879.5 cM
    36 matching segments
    Estimated number of generations to MRCA = 1.5

    They have 6 cM segments over 100 cMs and another 4 over 95 cMs.

    My Dad is 78 years old and the match is 88. We are positive about my father’s paternity but the match’s father abandoned his family in the early 1930s. My grandfather would have been 19 when the match was born, but his father (my great-grandfather) was extremely promiscuous (16 children by 3 different women that we know of) so that’s a possibility as well. I think these numbers point to a half-sibling rather than a half-uncle but would like your opinion as this is new to me and extremely confusing. There are big sections of blue but no big bars of green.

    I would be happy to email you the kit numbers if you would be able to take a quick look. Thanks!

  122. Hi Kitty,
    I have two people, we cannot figure out if they are my half brothers or Uncles. One of them I share 1883 cm with 47 segments with three segments over 100 cm and the other I share 2157 cm with 51 segments with three segments over 100 cm. I am under the impression there has to be 4 segments over 100cm to be considered half siblings? Also we all tested at 23&me.
    I feel so confused so I was hoping you could help shed some light for me. Thank you!

  123. Hi there,
    Love your blog. My father in law has been searching for his birthparents for over 20 years. He was adopted at a week old. I have been helping him for about 5 yrs. Recently, we had some good leads and we had someone that we thought may be his brother or half brother take the ancestry DNA test and sure thing it came back that they share 2176.9 cm and 64 segments. It says they are 1.4 generations. I am having a really hard time figuring out if they are full or half brothers. When I compare their kits on gedmatch doing the 1 on 1 comparison, there are a lot of green blocks and a lot of blue lines but there is also a lot of yellow. When I do the x chromosome comparison, there are a few smaller green blocks and a blue line and lots of yellow. The half brother or brother was born the same year as my father in law and so they cannot have the same mom (unless my father was born very premature which we do not believe was the case). To make this even more complicated is that we believe that my father in law’s mother and his brother or half brother’s mom are sisters. We have always believed that they share the same dad and their mom’s are sisters. Would this be the reason why his cm are higher for a half sibling and why there is more green on the regular DNA and X chromosome comparison tests? Can you please look at the kit numbers (how do I give you the kit #’s?) and let me know what your opinion is? I’d really appreciate any help with this and it would mean a lot to us. Thank you!

  124. Ok, yes that is the conclusion we came to. Is there any way using the gedmatch site that we can narrow it down to which sister it is? Any tips would be appreciated!

  125. Also, this was a little strange. One of my father in law’s matches came back at 575cm and 27 segs (this is his mother’s brother’s daughter-so his 1st cousin) but for his half brother the same match came back with 1094cm and 44 segs. That is a quite a difference. The other DNA matches that came back as 1st cousins are all the same range as his half brothers, ~ 1000cm. Would this mean that my father in law’s mom may not have the same mom as the rest of her siblings or could it still be 1st cousins for both since it’s still in the range for 1st cousins although opposite ends?

    • Windy –
      DNA inheritance gets more and more random beyond close family so by itself that 575 result is not significant. If more cousins on that side are low or that cousin matched others too low then worth looking at some more

  126. Hi Kitty,
    I’m trying to determine if my brother and I are full sibling or half sibling. Below is the comparison results from 23andMe.

    Gloria Green and Willie Hill
    Half identical
    2397 cM
    39 segments

    Completely identical
    651 cM
    31 segments

    • Full siblings.
      Half siblings will not share any fully identical regions (FIRs) unless their other parents are closely related

  127. Kitty, I’ve done my DNA, with My Heritage, Results are in;
    ____________ ___________
    Showing Nephew – Half Brother to me !!!!!!!!
    Shared DNA 23.2% ( 1682.1 cM) Shared segments, Largest 203.2 cM

    Would this be correct ????
    Thanks OAM

  128. Kitty, thanks for the reply, there are 33 shared segments, only the largest one is shown
    At 203.2 cM .
    How would I find out the size of the other segments?
    Thanks OAM

  129. Kitty,

    I was adopted as an infant and I have recently sent a DNA sample to Ancestry.com. I have discovered a close relative with 1363 centimorgans across 36 segments. We have been in close contact since this discovery and believe that we are half brothers as opposed to 1st cousins. A piece of this puzzle is his 1st niece who is the daughter of his brother. and I have 886 centimorgans across 29 segments. She is closer by @ 100 centimorgans than 2 children of his father’s siblings. Both his father and his father’s brother were in the same area at the same time but we believe we share the same father and the same uncle. Does this sound right to you?

    Thank you,

  130. Thank-you for your time and patience!
    The four largest segments are;
    Chromosome # 4. 203.22
    # 3. 168.38
    #.1. 159.54
    # 6. 148.48
    # 15. 138.62
    # 2. 137.26
    Kitty this is all new for me and a big surprise!
    Thanks again for your help.

  131. Kitty, my earlier message with the four largest segments for our DNA, some of them were wrong.
    The four largest segments are;
    Chromosome #4. 203.22
    # 15. 138.62
    # 3. 128.52
    #. 6. 114.37
    With four more above 70.97
    23.2% ( 1682.1 cM)
    Male and I share 33 DNA segments
    Largest segment 203.22
    Would we still be half brother and sister?
    With the same father, his or mine?
    Thanks again, for all the time and love you put into your work!

    • Yes I am still suggesting half siblings, same dad since such large shared segments.
      And thanks for the compliments. I love this stuff and try to make it understandable to others.

  132. Hi, Kitty!

    I recently found several “Close Family–1st Cousins” matches on ancestry.com. We have between 1,484 centimorgans shared across 49 DNA segments and 2,194 centimorgans across 63 DNA segments. Are these matches likely half-siblings or full?

    I also found my maternal aunt. We share 1,797 centimorgans across 77 DNA segments. Since my aunt and I share no close matches on ancestry.com, all of my other close matches must be from my father’s side.

    I’d love to know your thoughts on this. Thank you so much!

  133. I have a question. If siblings had say the same mother but their fathers were brothers, how many centimorgans would they share? Are there any matches that would make them appear to be full siblings when they have different but closely related fathers?

    • We call this a three quarters relationship. more shared DNA (about 2200cM) than half sibs plus some FIRs but not as many as full sibs. Their matches would be the same as full sibs, the difference would be in the one to one comparison of their results.
      If they are not tested at 23andme then they need to be uploaded to gedmatch, preferably Genesis to see this.
      It would be similar to this case

      • I have almost the same question as Terri. My sister and I sent our DNA to 23andme and got a 55% match. We have reason to believe we may be half siblings, but is that possible with that high of a match? If we are half siblings our fathers would be father and son. Could we be half siblings and still have a 55% match?

        • These days you can see the fully identical segments at 23and me by using the DNA tab in DNA relatives which will answer your question.
          Sharing 55% is surely a full sibling however

  134. I appreciate all of your patient answers here, and I’ve read them all. My question: How can maternal half siblings, one male, one female, have some fully identical regions on the X? The X match is 157.6 cM; total match is 1766 cM. The fathers were of distinctly different populations.

    Thank you.

    • There is no such thing as a fully identical region on a male’s X because he only has one X chromosome; and it is from his mom. So it gets called fully identical on some sites but that is a misnomer. Normally fully identical means bothe chromosomes match but there is only one here.
      These half siblings got that matching X from their mom.

  135. Hi Kitty,
    I’ve just carried out a Genesis GEDmatch comparison for my sister and I.
    Based on the results below, would you agree that we are half siblings?

    I would say it’s pretty conclusive that we are, but I would be grateful for a second opinion before breaking the news to my sister.
    Largest segment = 106.2 cM

    Total Half-Match segments (HIR) = 1544.1 cM (43.1 Pct)
    Estimated number of generations to MRCA = 1.6

    48 shared segments found for this comparison.

    617002 SNPs used for this comparison.

    63.8 Pct SNPs are full identical

    The next largest matching segments are as follows:
    80.5 cM
    77.4 cM
    74.0 cM
    60.5 cM

    • Gerry –
      Those numbers say half siblings. You do not share enough DNA to be full siblings.
      It could also be an uncle/niece relationhip if you have an older sister whose child she or you could really be … The numbers there would look about the same as this, two siblings with different fathers.

  136. Perhaps you can shed some light On this topic for me. My (half)brother and I have the same mother, but two different fathers. Our centimorgans are 2,074 which I am told is a rather high amount for 1/2 siblings. The kicker? we were both adopted. He knows his father, i do not know mine. Where should we start looking? Help?!

  137. Hello Kitty

    I’m sorry I did not explain very well in my last post. Unfortunately, I do not have the facility on my iPad to create a spread sheet, and am not sure I would know how to do it (well in my 70s). I have previously given you access to our FF accounts and Gedmatch, and could do the same for my niece if you think that would help.

    Brief recap: I grew up with two brothers, all of us believing we had different fathers. Recent DNA testing with my older brother showed we were full siblings. My younger ‘half’brother’ is deceased, so his daughter (my apparent half-niece) agreed to a DNA test. Which were the results I posted. Y testing showed one result which could be related to the family of my stepfather (my deceased ‘half’-brother’s presumed father) Hence my query. The results for my half-niece seem very borderline, and I wondered if it was possible that our father could have been a brother of our stepfather?

    My son matched with my full brother as a nephew with well over 1900 CMs, but my half-niece only matched with my full brother with 1364 CMs. However, she matched with me with 1482 CMs.

    Kitty, am I able to upload FF results to GEDmatch or Ancestry? I have not been able to find anything to tell me I can, or how to.

    Many thanks for your patience and help.


  138. Hello again Kitty

    I have looked at the spreadsheet you recommended, but, unfortunately, find it beyond me. I have looked at the comparison of myself and my half/full niece on Family Finder though, and I hope I have read it properly.
    There are 43 Chromosome matches over 7Cms. The highest is 122.28
    All 5 X Chromosomes match. 3 over 7Cms. The highest 59.45Cms.

    Many thanks.


  139. Pat
    I will email you. Most likely she is your full niece and your other “half” brother was also a full brother. Can you get any cousins on the side of his supposed Dad to test?

  140. Kitty,

    My mother-in-law was adopted. She found her mother about 20 years ago, but her mother was unable (or chose not) to tell her who her father was. We suspect that her father was a relative, perhaps even a half-brother. I ran the “Are Your Parents Related” tool on GEDmatch and received results that I can’t really interpret, other than a statement found at the bottom of the report, ” This analysis indicates that your parents are probably related within the last several generations.” Would you be willing to take a look at the report, etc.? Thanks so much!

    • Steve,
      I will email you. Cece Moore is the expert on this but I will happily help. Mutliply the amount of shared DNA in that report by 4 and look it up here:
      But best to have some expert advice.
      I know our society has a big taboo on this but the DNA is usually OK as long as it is not a repeating pattern over many generations. Best to double check that she has no health risks from this by testing at 23andme and /or double checking at promethease (but be careful, it is tricky to use and not everything is necessarilly so, check with your Dr if anything is found before taking any action)

  141. Hi Kitty,
    I would love your advice. I’m looking at two very different ethnicity results on siblings who are thought to be full siblings. Their DNA Match quality shows:

    33.1% (2,398.7 cM)
    40 Shared Segments
    174.7 cM

    Is that within the normal range for full siblings? Could they be half-siblings? What it their mother had an affair with their uncle? (Purely hypothetical, no evidence or suggestion of this.)

    I’d run them through an additional tool, but don’t have the full report for one of them currently. Their ethnicity results are 50% the same (matching the known ethnicity for their father), and 50% vastly different (50% Western Europe vs 25% Eastern Europe + 25% Middle Eastern). The latter makes no sense considering how far we can trace back the family tree.

  142. Dear Curious –
    Those numbers are 98.7% full siblings according to the DNApainter calculator.
    Slightly on the low side according to the DNAadoption predictor.
    Compare them at GEDmatch to know for sure as explained in this article.
    Ethnicity predictions are still an emerging science and are not all that accurate yet. Each sibling only got half the parents DNA and they can get quite different ethnicities in that mix.
    This slide compares me and my known full brother and we have some ethnicity differences
    Which ancestries are different? Send me more information via my contact form if you are still worried about it after reading this article

  143. Kitty,
    After my wife ordered me an Ancestry DNA kit for my birthday this year, I was shocked to find a “close relative – 1st cousin” that I had never heard of.

    As I dug deeper and made contact with this lady (she’s 39 I’m 35), I discovered that she did not know who her biological father was. Come to find out we are from the same town/county, and one of our shared DNA matches (2nd Cousin) on Ancestry pointed her to a family here in my hometown as the only relation in our state, let alone area.

    I have known this family my whole life and when confronted about it, my mom confirmed that my biological father was from this family, and not the man I’d known for 35 years as my dad.

    I’m almost certain this lady is my Half Sister based on our DNA results, but wanted to confirm with someone that knows more than I in the field. From what I can tell our numbers are on the higher side for Half Siblings, but I can rule out full sibling as she is biracial and I’m not. Any help would be greatly appreciated! Below are our results from Ancestry and gedmatch:

    Ancestry: 2,293 centimorgans shared across 46 DNA segments
    Gedmatch: Largest segment = 215.7 cM
    Total of segments > 7 cM = 2,366.3 cM
    30 matching segments
    Estimated number of generations to MRCA = 1.3

    396448 SNPs used for this comparison.

  144. Yes she is your sister. Those numbers could even be a full sister although your situation suggests half with a shared dad
    I have an article here on telling full from half soublings …

  145. Hi Miss Kitty, Just was blown away by some 23andme results for me and my brother. We were predicted to be half siblings. I’ve since uploaded the data to GedMatch Genesis. My results are as follows:
    Largest segment = 69.8 cM
    Total Half-Match segments (HIR) = 1960.6 cM (54.7 Pct)
    Estimated number of generations to MRCA = 1.4
    64 shared segments found for this comparison.
    482480 SNPs used for this comparison.
    No FIRs.
    Can you confirm – this indicates half siblings? I will have some more investigating to do as I know that my mother saw a doc to assist with some fertility issues back then. Also, from your experience, there is no likelihood this test could be wrong? Are they ever wrong? Thanks for your help.

    • The lack of FIRs means you are not full siblings, as you have already realized. Also the number of shared CMs is consistent with a half sib
      DNA does not lie.
      Get a patternal.side cousin or two to test. See if they match either of you

  146. PS – the above was autosomal. Here are X chromosome results.

    Largest segment = 103.0 cM
    Total segments = 145.1 cM (74.0 Pct)
    3 shared segments found for this comparison.
    9794 SNPs used for this comparison.

  147. My son was matched on Ancestry.com to a female that was a Close family- 1st cousin match. They are only 5 months apart and I had a brief affair with her mother. I’m confused why they are listed as 1st cousins and not half-siblings. There is a very slight chance that my brother who was living in the area at the time could be her father. But I’m not sure. Her mother was half Italian and I’m full Italian. I’ve been on an emotional roller coaster ride ever since!

  148. Dear concerned,
    Congratulations! That is how ancestry lists half siblings- Close family- 1st cousin, they never say half sibling. Partially because it is very hard to tell half siblings from niblings or high first cousins from the total centimorgans. But the facts you give make you her likely father. If you take an ancestryDNA test, you will know, parent-child relationships are unmistakable in the DNA
    Read this to understand why half siblings are less clear
    If your son and his half sister both upload to Gedmatch.com then I can usually tell the difference and that article explains how

  149. Kitty- Need some help. Did Ancestry because I knew nothing about my dad. CAme back with a close relative/first cousin. After research he matched neither moms side or dads. After further research me, this person and 1st-2nd cousins are all looped together but bargain not through my moms side. Neither of these 3 people connected with any facts about my last name/dad’s side. I know very little about my dad….divorced before i was born, no none of his relatives etc. After giving up search i spent a few more days. Comes to be is me and close relative share 2084CM over 45 Segments. The other w connections are all connected via his dad’s side of family. Current theory is this guy is actually my half brother. My mom states she does not recall this name but wouldn’t you say the numbers prove differently? Is there any other tests or something else that can be done to verify. Suspected dad is dead as well as any siblings. By contacts on Ancestry the next 2 closes relations scored 400CM over 25 Segments

    • Dear GFred,
      It sounds like your bio father is not the expected person. Your mother may just not remember if it was a difficult time in her life. Yes you have likely found a half brother. If you both upload to GEDmatch I will have a look for you.
      There is much help listed on this page:
      finding your bio dad is like an adoption search but a little easier.

  150. I believe I uploaded to GEDmatch. I am not sure about the other party. I have an assigned kit number. Does this mean I have done this part successfully?

  151. Hi Kitty–I am so confused and hope you can help. I did Ancestry DNA along with my full brother. There was a woman who showed up for both of us as a close family with 1460 across 38 segments and for my brother it was 1670 over 40 segments. We have spoke and she feels as if she is our 1/2 sibling however to make a long and very interesting story short, the timeline does not add up. She would have been on my Dad’s side. I was sure of it as well but again the timeline does not add up. I have my raw data and she is trying to get hers and she also sent me a sibling to sibling DNA test to test again but again–the timeline doesn’t make sense. HELP! Who is she with those numbers?

  152. Kitty ,

    A little help for my confusion please. I recently tested from Ancestry and came across a 1st cousin match that says she was placed up for adoption. we have since learned she might be a half sibling on my mothers side. we both put our raw dna to gedmatch along with my Full aunts dna . when I do a one to one comparison on both of them it shows ALOT of green and not much red but centimorgans are 1,714.1 cM with the longest being 107.0 cM and MRCA = 1.5 . If based on the green like graphs above I would think full siblings but with the Cm half siblings? Please Help!!

  153. The green are not long bars but single lines or occasional small collections of lines which just indicate that they are from the same ancestry. The numbers suggest she is your aunt’s half sister by her mother (since not a full X, right?).

  154. Dear Kitty,
    My brother and I did Ancestry DNA tests. Ancestry designates the two of us as “Close family” – 1st cousins. Our shared DNA is 1729 Centimorgans across 63 DNA segments. A paternal 1st cousin also tested through Ancestry and is listed as a 1st cousin to my brother. He is listed as no match to me. a few other cousins show up as different levels of cousins for my brother and myself. For instance, several appear as 2nd cousin to me and 3rd, 4th, 5th to my brother. I am assuming from this that my brother and I are 1/2 siblings with different fathers. Or, am I oversimplifying? Thanks you!

  155. Dear Judy,
    Well done figuring this out. Yes your brother is your half brother and your father is not the expected person. Take a deep breath. Can you ask your mother about this?
    The different levels of cousins can be just the randomness of DNA recombination but perhaps your bio dad is related to the father who raised you. Are there matches you have but not your brother? They would be the key to finding your birth dad.

    You can use DNA to find your bio dad. The same techniques as adoptees use but easier with only one parent to find and a half brother test see https://blog.kittycooper.com/dna-basics/help-for-adoptees/

  156. Dear Kitty,
    I thank you for this information and clarity.
    I am 71 and my brother is 75 and our parents and all aunts/uncles died 15+ years ago. I do have matches that my brother doesn’t have and am not familiar with those family names. Even before the truth dawned on me, I messaged those matches to see how we might be connected, but have not heard back from them.
    My brother doesn’t know the outcome of the tests yet. On an emotional level, I am digesting and reluctant to “out” my mother to him or his children at this point. I will look at the link you sent for adoptees. But would I be able to find out who my bio dad was without more info? A couple other questions — given the Ancestry data and the clarity you’ve provided, does it make sense for me to upload mine and my brother’s raw DNA data to GENmatch? Also, I ordered another DNA kit from Ancestry recently when they were on sale and have that unused kit on-hand. Would doing a second test provide any different data from the first, or am I on solid ground with the first results? Again, I am very grateful for your response. What a valuable service you are providing.

    • Keep that extra DNA kit for when you find a paternal relative you want to test. Testing again will not change the results.
      Yes upload both you and your brother to all the sites that take transfers. Family tree DNA, My Heritage,and GEDmatch. You may also want to purchase 23and me kits for the two of you.

  157. Hi Kitty–I did Ancestry DNA along with my full brother. There was a woman who showed up for both of us as a close family with 1460 across 38 segments and for my brother it was 1670 over 40 segments. We have spoke and she feels as if she is our 1/2 sibling however to make a long and very interesting story short, the timeline does not add up. She would have been on my Dad’s side. I was sure of it as well but again the timeline does not add up. I uploaded our raw data to GED match and chromosome 23 shows 194.8 CM//chr 1 was 189.2 cm//chr 3-8.5 and 151.4//

  158. Yes those numbers say she is a paternal half sibling. If you were female, then you could compare X as it would match completely for paternal half sisters.

  159. Kitty–My possible half sister and I did a sibling test through BIO-GENE. It came back with Combined Siblingship Index: 0.6675. Yet ancestryDNA matched us as 1460 across 38 segments and for my full brother with her it was 1670 over 40 segments. I uploaded our raw data to GED match and chromosome 23 or X shows 194.8 CM//chr 1 was 189.2 cm//chr 3-8.5 and 151.4//. Why do the results from GED match and Ancestry DNA confirm we are 1/2 sisters yet BIO Gene came back as inconclusive? Will my children being tested help? What should we do next? Is there someone who could look at our raw data to confirm or should we do another sibling to sibling test elsewhere? Thanks so much. If you have venmo or other let me know and I will send you enough for that bottle of wine. Thanks again.

    • The commercial sibling tests do not test as many data points as ancestry so are not very reliable past very close Family

      • So it was a waste of money then. I wonder why they claim that their tests are used for both legal and home testing and test with 50% more sibling markers than the industry standard. It says they tested 34 locus. Assuming a locus is a data point, how many does A.DNA use? I am sorry with all the questions. I am just perplexed.

  160. Hello!
    I recently made a “Close Match” on Ancestry with 1,662 cm and 47 DNA segments. I uploaded this info to GEDMatch and have no clue what I’m looking for. I am wondering if this is a half-sister? Any help would be much appreciated!

    Largest segment = 175.9 cM
    Total of segments > 7 cM = 1,731.9 cM
    34 matching segments
    Estimated number of generations to MRCA = 1.5
    399644 SNPs used for this comparison
    Chr 2
    94.7 cm 11,193 SNPs
    Chr 8
    22.8 cm 3,070 SNPs
    Chr 12
    175.9 cm 20,050 SNPs
    Chr 13
    41.6 cm 4,150 SNPs
    Chr 15
    121.8 cm 12,274 SNPs
    Chr 18
    19.9 cm 1.458 SNPs
    Chr 19
    92.3 cm 6,971 SNPs
    Chr 22
    41 cm 3,578 SNPs

    • Hello!
      Thanks for the response. Largest 4 segments are:
      175.9, 121.8, 105.0 and 104.0

      I also did a X one-to-on comparison and got this:
      Chr Start Location End Location Centimorgans (cM) SNPs
      X 2,321 154,886,292 196.1 15,716
      Largest segment = 196.1 cM
      Total of segments > 7 cM = 196.1 cM Actual.

      • I forgot to mention, my aunt and daughter matched to this person on Ancestry as well. My aunt matched to her as a “Close Match.” The cMs shared with my aunt and this suspected half sister were about 1,700 cMs. This suspected half sister also matched to my daughter as a “First Cousin” at 921 cMs shared across 34 DNA segments.

  161. Assuming you are a woman and your aunt is your dad’s sister, those numbers say she’s your half sister, same dad.

  162. I’ve been trying to research how common it may be to share more than the average number of cm with a half sibling and haven’t really found anything definitive. My half sister and I share the same father. We share 2,488cm and 33.4% DNA.

    These numbers are higher than any “cap” I can find online. I find it very interesting and wish I could find a similar comparison or what the odds are of sharing more than the average…

    • Melissa –
      That amount of shared DNA is in the range of full siblings, is that a possibility? Or could the mothers be related? Are there any fully indentical regions (shown in 23andme and GEDmatch only)
      Where are those numbers from? If they are from 23andme they include the X which will increase the amount shared. If they are from family tree DNA they include many small segments which also increases the amount
      The online charts are based on the sum of segments > 7cM with no X. Can you tell me what that shared amount is for the two of you?

  163. Question: My father told me before he passed that he may not be my father and that my true father is actually my Uncle (his brother)! That being said my sister and I did the Ancestry DNA and uploaded the raw DNA to GEDMatch and I still can’t tell are we half or full sibs??? We share 2294 centimorgans across 63 DNA segments according to ancestry. I don’t understand the chart on GEDM, it says 47 matching segments. My sister and I are both related to both possible fathers, so how can we tell? Thanks for your help!

    • Dear sisters,
      You could be either. That is a low total for full siblings but within the range (DNA painter’s calculator says about 34%).
      Can you test more family members, namely your uncle or his children?

      If you two both upload to the GENESIS site, you can find the total of your fully indentical segments which may help figure this out. You will share more FIRs with a full sister than a half sister whose father is your dad’s brother

      • X-DNA 1-TO-1 Comparison

        X 2,703,633 to 52,067,217 82.6 cM 5,612 SNPs
        X 61,992,011 to 154,916,845 105.1 cM 7,997 SNPs

        largest segment = 105.1 cM
        Total Segments = 187.8 cM (98.9 Pct)
        2 Shared segments found for this comparison
        13858 SNPs used for this comparison

        Since the blue bar was not a solid blue bar and contains a section with no match and a large gap between adjacent SNPs and the two possible fathers are brothers, what do these X results mean? Do we have the same father or are we half sibs? We share a mother for certain.

        Also here are our FIRs:

        Largest segment = 99.0 cM
        Total Full-Match Segments (FIR) = 851.8 cM (23.8 Pct)
        33 Shared Segments
        397252 SNPs used
        69.6 Pct SNPs are full Identical

        We share 2294 cM across 63 DNA segments according to ancestryDNA.

        Thanks for your help.

        • The total FIRs suggest a full sibling match. Also the X is almost a full X. I have seen tiny breaks like that between full sisters before. Usually it is because of the use of a different chip else a small error.
          Please do the X one to one on GENESIS, it may fill in that gap.

          • Hi, thank you for looking at this, these results are all from the Genesis program Genesis X-DNA One-to-one Comparison.

          • Sorry to bother you again, but what do you mean when you said “use of a different chip”?


          • It might be possible that my dads brother is my father and not my uncle. My brother and I show 2208 cm across 63 segments on ancestry.com which appears low. So I did a little research on gedmatch genesis and this is what I got. Also the chart on the one and one comparison showed lots of black on the bottom instead of the greyed out large gap color. It was either black or the bright blue/purple on the bottom. Does this determine if he is my full or half sibling?

            Largest segment = 131.8 cM

            Total Half-Match segments (HIR) = 2244.2 cM (62.576 Pct)
            Estimated number of generations to MRCA = 1.3

            54 shared segments found for this comparison.

            423414 SNPs used for this comparison.

            66.599 Pct SNPs are full identical

          • Holly –
            Yes from those numbers it is possible that your Dad’s brother is you bio father but it is also perfectly likely that he you have the same Dad. If any children of the brother would test tat would tell you.
            (I deleted a previous comment because I had missed the fact that it was not 2 sisters but rather a brother and a sister so the X is irrelevent)

  164. If me and my cousin (she is first cousin to me on my mothers side and second on my fathers side) share FIRs are the shorter green segments those which I match her on the second cousin side? Also is there any way to know the cm length and the location of those green segments?

    • The green bars are fully identical regions (FIRs). That is where you share DNA with her on both chromosomes at that position. So you have matching DNA from both relationships, both sides.
      The new GENESIS site let’s you get the actual numbers for those FIRs and it will be integrated with Gedmatch eventually but you could both upload there.

  165. My next closest match on Ancestry after my daughter (3,400 cm’s) is a Close Relative to 1st cousin, with 2,210 cm’s across 66 segments. I am an adoptee searching for birth father; birth mom has been found, so we know my father is on this side of the family. The only likely option as my father would make my close match a 1st cousin. But we share such a high level of DNA it seems unlikely he is my cousin. I match with another ‘1st cousin’ and we only share 900 cms. The GEDmatch site is overwhelming and not very clear how to upload and test the data. Is there a concise click by click instruction sheet somewhere? Also, CAN 1st cousins share 2,200 centimorgans?

  166. Hi kitty, I’m looking for your expertise help once again!
    I see you are very busy, what would we all do with out you!

    When you find time, would you have a look at #1 and # 2 , both females!

    #1 – J we grew up as full sisters!
    Came back as Half sister- Niece

    23.5 % (1,700.7 cM)
    42 shared segments
    181 cM Largest segment

    #1 112.8 cM
    #2. 92.8
    #4. . 101.3
    # 10 181.0
    #17. 90.6

    # 2 M. I never knew about, until I had my DNA done, months ago
    Niece- half sister
    Shared DNA 28.3% ( 2,053.3 cM)
    35 shared segments
    Largest 141.5 cM

    #1 chromosome. 91.0 cM
    #2. 122.0
    #6 131.6
    #11. 101.6
    #12. 102.3
    #13. 100.4
    #15. 141.5
    #16. 114.3
    #17. 123.5

    Kitty, #1-J and me, same mother, different fathers.
    #2- M and me, Her father and my mother.

    Am I an aunt to either or a half sister to both?
    I hope this makes sense to you!
    Thanks again

  167. The post you need to look at is:
    These both look like your half sisters. #1 is same mother and #2 is clearly a half sister, the same dad (large segments and larger total)
    Remember the DNA companies are only guessing at the relationship based on the total cMs which are the same for an aunt and a half sister. To tell them apart I look at segment sizes and the X match.
    Check the X on #2 – paternal half sisters will share a full X. Also have you checked both kits for related parents?

  168. Kitty, thanks for your quick Response!
    I will look at the post, that you suggested!
    Our three, DNA KITS were from My Heritage!
    Kitty, make time for yourself!
    Thanks once more,

  169. Hi Kitty,

    I have recently done DNA tests with my sister, brother and 2 daughters. The results would suggest that my siblings are actually my half siblings.

    I have only around 1750cM in common with my sister and my brother. They have 2600cM in common with each other.

    My daughters have between 750 and 1000cM in common with my sister and brother.

    The one on one test on GEDcom between my brother and I shows the following: There are not a lot of green patches.

    Largest segment = 129.2 cM
    Total of segments > 7 cM = 1,951.4 cM
    53 matching segments
    Estimated number of generations to MRCA = 1.4

    My mother is ADAMANT that my father is my father. I look like my mother so there can be no dispute that I am hers. I don’t look like my father and I am much taller than anyone in the entire extended family.

    1) How do I calculated the shared DNA figure that everyone refers to?

    2) The info looks fairly conclusive to me. Is there any way it can be wrong? Is it possible that I am a freak of nature and carry very little of my dad’s DNA?

    3) Is there anything in the testing which is CONCLUSIVE that I can rely on?

  170. Forgot to Add Data with my sister:

    Shared Segments 55

    Sis Me 1 24.41 3668
    Sis Me 1 20.58 5000
    Sis Me 1 13.53 2034
    Sis Me 2 21.3 4382
    Sis Me 2 1.98 800
    Sis Me 2 27.75 7248
    Sis Me 2 43.06 10859
    Sis Me 2 33.06 8484
    Sis Me 2 33.08 5544
    Sis Me 3 13.4 2188
    Sis Me 3 25.54 6900
    Sis Me 3 21.12 3968
    Sis Me 3 16.93 4200
    Sis Me 3 68.12 12175
    Sis Me 4 108.69 24051
    Sis Me 5 5.92 1300
    Sis Me 5 6.14 2000
    Sis Me 5 1.23 500
    Sis Me 5 51.2 11298
    Sis Me 6 36.4 6358
    Sis Me 6 5.4 1100
    Sis Me 7 30.76 5991
    Sis Me 7 32.74 8200
    Sis Me 8 21.4 4656
    Sis Me 8 37.98 9295
    Sis Me 8 20.57 3841
    Sis Me 9 75.97 16555
    Sis Me 9 23.24 4975
    Sis Me 10 20.55 3759
    Sis Me 10 9.54 2800
    Sis Me 10 24.13 5700
    Sis Me 10 1.54 600
    Sis Me 10 20.84 3399
    Sis Me 11 21.38 4781
    Sis Me 11 44.46 12300
    Sis Me 11 31.48 9100
    Sis Me 12 40.01 10800
    Sis Me 12 80.42 14943
    Sis Me 13 105.35 24856
    Sis Me 13 6.35 707
    Sis Me 14 40.61 10094
    Sis Me 14 24.62 4040
    Sis Me 15 72.1 15060
    Sis Me 15 45.33 6474
    Sis Me 16 27.05 4525
    Sis Me 16 9.95 1316
    Sis Me 17 63.66 11273
    Sis Me 17 6.03 667
    Sis Me 18 75.55 15454
    Sis Me 19 17.22 2345
    Sis Me 19 13.58 2668
    Sis Me 19 17.37 2636
    Sis Me 20 30.64 5205
    Sis Me 20 10.31 1900
    Sis Me 21 58.99 10222
    Sis Me X 82.97 8750
    Sis Me X 5.47 650
    Sis Me X 62.68 5167

  171. Hi Kitty
    Im on the path of DNA having learnt my mother was adopted and believe I have found a half cousin on what I believe to be my mothers Brothers side. The half cousin is willing to test but as its been a secret for 70yrs no one else is…Is there a test (m/f) that can be taken to show this is correct or not ?

  172. Hi Kitty – I am adopted, and I believe I have found my birth family thru Ancestry.com. A newfound relative recently did her test and it came back today at 1624 Cm across 68 DNA segments. It noted us as “Close Family” but suggested 1st Cousin. We don’t know yet exactly how we match up above her generation… Given the Cm result, I am thinking we are half sisters and not first cousins. What do you think?

    Her mother is still alive and lived in the state where I was born. She was a teenager when I was borh, which aligns to what I have been told about my background. There is trepidation about talking to her about this… we will get there eventually, but haven’t brought her into the conversation yet.


  173. Okay, I have a slight dilemma here. I have a match that shares 763 cM with me and she shares 1168 with my mom. Sadly her mom is deceased so we can’t test her. But we are wanting to know if it’s possible, with those high of numbers that her mom and my mom are actually half siblings? I am assuming if we did test her mom when she was alive, that she would be in the range of 1500-1700 with my mom. It’s highly likely my grandfather and her grandmother had an affair. But we just can’t pin point the numbers. I’m leaning more towards our moms are half sisters. What would the numbers be if my grandfather’s brother had an affair with her grandmother? Wouldn’t our numbers be lower in shared?

  174. Hi Kitty,
    You have a wonderful blog, full of insights and advise.
    I would like to pose my recent GedMatch work to see if you agree with my thesis that we do in fact have a common Mother please?
    Uploaded my Ancestry DNA to GedMatch, along with projected half-siblings Ancestry’s data, for one to one, and X DNA one to one matching.
    1:1 Total cM is 1664, we match with full and half matches on 1 – 21, na on 22. Largest is 105.
    X DNA 1:1, we have full matches Green over Blue, total full matches is 107, largest is 88.4, next largest is 19.0.
    We are 18 months difference in age.
    I do not understand why GedMatch conveys 1.6 for the generational difference. May I ask you to comment on your belief that the X DNA confirms a common mother, and your thoughts on the 1.6 generational separation please?
    Many thanks in advance,

      • Hi Kitty,
        Thank you for the reply and reference.
        A follow up question please.
        In the joint research that the target male half sibling and I have conducted, we find that his Mother (target Birth Mother) only has two Brothers, and No Sisters for siblings. We do have a high cM match with the Granddaughter of one of the target Birth Mother’s brothers, as a 1st Cousin Once Removed.
        Does this additional information in your estimation place more weight on the prediction that the half male sibling and target Birth Mother are the correct family targets?

        Thanks again,

  175. Hello I need some help as I have quite a mental learning block when it comes to DNA. Lol. To our shock, kind of, my daughters 23andme recently came back with a close relative. 23 and Me says it could be an uncle, granpartent and has him listed as her grandson but she is younger and has had no children.

    This match indentifies as a male and they share 1801 cm and 38 segments with the longest being 180.25 cm with nothing on the X chromosome. Halos are differnt mothers(I only had one child-my daughter) and I don’t know my daughters father hallotype.

    Their ancestry is somewhat similar with European ancestry but he is 31% Italian and my daughter has none. He is also matched with my daughters other close matched second and third cousins and they are all confirmed family and have no Italian heritage either.

    My ex cheated on my several times so god only knows what has happened. My daughter has an uncle and a grandmother on her fathers side but close confirmed matches to them do not show any Italian either. So the likelyhood of this being an grandmother or uncle is somewhat unlikely but I could be totally wrong as well. I do believe this match is indeed a male because his profile list mother and father halo types. Please advise when you can. Thank you so much.

    • Sorry forgot to write the this male match is also matched with confirmed cousins on my daughters father side . He has no matches on my side.

      • Wow thwnk you for getting back to me so quickly Kitty. Her total dna match with this person is 24.2% but 23andme listed him as a grandson..how they heck do they do this? Also do you think we can safety rule out first cousin?

        Now I don’t know whether to throw up or throw something. Lol that sob! Lol

        • The testing companies assign relationships based on the total cM shared. It cannot tell a half sib from an uncle or grandparent, all about 25%… That is why I did the study reported on in that other article.

  176. The man I was told is my father is certain he never met my mother. He told me he believes I’m his uncle’s child. He did not want to do a dna test but his daughter and I matched as close family on ancestrydna. We share 2201 cm. His brother is also on there and we share 1700cm. If I’m understanding correctly the numbers are too high for her to be my second cousin and she would be my half sibling?

  177. Hi Kitty! Thank you for blogging about all of this. It’s been so helpful for me and my very new journey into all of this.

    My brother and I both uploaded our RAW data – he tested through Ancestry and I tested through 23andMe.

    Largest segment = 82.7 cM

    Total Half-Match segments (HIR) = 1871.7 cM (52.198 Pct)

    Estimated number of generations to MRCA = 1.5

    67 shared segments found for this comparison.

    139368 SNPs used for this comparison.

    59.868 Pct SNPs are full identical

    total cM: 1899.8
    overlap: 66752

    I understand that having our cM at 1899.9 would put us in half-sibling range – but do the other numbers support that? We’ve tried to calculator you’ve mentioned, and it definitely points toward half-siblings. Us being half-siblings would be a complete and utter shock. Any information would be helpful.


    • Look at the one to one image comparison. Full siblings will share numerous fully identical segments aka regions (FIRs) which appear as green bars as per above images.
      On gedmatch genesis, you can also check the FIR box in the one to one comparison to comfirm the lack of FIRs

      • It says “No shared DNA segments found

        139368 SNPs used for this comparison.” The image looks closer to the half-siblings you’ve shown. So, that is likely what we are, right?

        • Yes., sorry, you have different biological fathers. Have any paternal side cousins tested so you can narrow this down? In some cases where the dad was infertile, sperm donors were used … in that case neither of you would match your father’s relatves.

  178. Help Kitty!!
    My sister bought 23 and Me kits for christmas. The website lists us as half-siblings with Half identical: 2165 cM & 63 segments. In addition it lists Completely identical: 176 cM & 11 segments. For example under the X chromosome….
    length SNP
    me / sis X 13.20 915
    me / sis X 47.71 4250
    me / sis X 35.99 2519
    So are we half-sisters? And if so which parent do we share?

  179. I have searched high and low for something regarding DNA on sibling cousins.
    My brother and I received a shocker on FamilytreeDNA… 1948 shared cms (half siblings). We thought we had the same dad. We are adopted, so it’s hard for us to get answers. A lot of things I read put half siblings averagely at 1700 cm, if we are at 1948, could it be that our dads were brothers? My birth mom a long time again said that our dad’s brother was very flirty with her. So what would one expect to see for half sibling/ cousins in the cm dept?

    • Marcella, sorry for your disappointment. If your fathers were brothers you will see a few FIRs just less than full siblings, shown above, so please upload to Gedmatch genesis and compare there

  180. I am new to all of this and was hoping for some guidance. My whole family did their DNA with Ancestry with the exception of my one brother. Me and my sister only share 2100 CM and it seems low? What could this mean? My Father died a couple years ago so we cannot test his DNA any help would be great I am very nervous and wish I never submitted this now…

    • Greg –
      It is perfectly possible for full siblings to share only 2100 cM (18% probability). If you both upload to Genesis GEDmatch you will be able to see the FIRs as shwon above if you have the same father.

  181. My husband was adopted many years ago with the adoption being done privately so we had little information regarding his original parents – a DNA test through Ancestry indicated a 1st cousin/Close relative with 1,929cM across 65 segments – we have contacted this woman who was also given up for adoption ( also a private adoption ) about 18 months before my husband was born – she advised she did apply for her original Adoption Notice ( could not obtain a Birth Certificate )& found her birth family – her mother had died but she did gain information re 4 siblings who were raised by herself & her partner who were evidently her parents as well ( the eldest born 2 years after my husband) – a friend has told us this a high reading for a 1st cousin however as she cannot be a sibling according to this info what other reason could there be?

  182. Hi! I did a siblingship test with Bio-Gene between my two daughters and a sample from me. The CRI was .13 and the probability of full sibingship was noted as 11.8%. Is this conclusive that they are only had siblings?

  183. Hello,
    Although this might seem obvious, I and my new found biological brother both took Ancestry DNA and was informed of our match as immediate family. Our shared centimorgans are 2322.
    We want to determine if we share the same father, as I’m adopted) I also share DNA with this brother’s 1st (462 cm across 23 DNA segments) and 2nd cousins.( 285 cm across 12 segments) May I assume we then share the same father since we have multiple hits on the same side of the family?

    In addition I share DNA ( cousins) on my brothers same side of the family.

    • Yes that is a good assumption. That is a very high amount to share with a half sib, possibly your mothers are related or it is due to the randomness of DNA.

      • Thank you for taking the time to reply. Yes, in fact we do share the same mother, and I assume from your above response, the same father.

        • If you match cousins from both sides of his family then same mother (which you knew) and either same father or your fathers are brothers. Best if you both upload to GEDmatch GENESIS and see if you share FIRs like in this article (the green bars)

  184. If 2 half brothers on their fathers side test their y-dna at the 37 marker, would their numbers match or might they be different. They match at 24 out of 37. Are they half brothers.

    • If they have the same dad they should match at 37 of 37 possibly 36 or 35 so matching only 25 out of 37 means not the same Dad but are you sure both have tested all 37? And that all results are in?

  185. Hi, what a great source of info here! My question is (hopefully) simple. Is it possible for me to be a full sister with someone with whom I share 1697cM, or does this number absolutely rule that out? We both tested through Ancestry.com. Does this mean that I have a different father from my sister? The only matches we share are labeled as being on our mother’s side. Ancestry also showed me that I (and NOT my aforementioned sister and NOT my confirmed mother) have a mystery female relative sharing 1839cM with me. She was born 9yrs before me when my parents were 10 years old. Does this mean that I have a different father from my sister? Thank you!

    • It seems like you have figured out that you and your sister have different fathers. Your 1839 match could be an aunt or a half sibling. Best to copy the information on her tree before you contact her and then go slowly and carefully. Read through some of the suggestions here:
      In my experience people are less freaked out by a man fathering a child out of wedlock unless it is their father and he was married at the time.

      • Thanks, Kitty! I am not looking so much to establish contact with my mystery relative as much as updating my own knowledge of my own history. I would love to have a relationship, but don’t want to cause anybody any pain. I don’t even want to share this info with my known family right now. I will definitely be taking it slow as I feel like it will take me a long time myself to process all this! I will read the dnaadoption info and always be grateful for your quick response.

        • Just to clarify—an 1839cM match would have to indicate a FULL aunt, meaning someone with the same biological grandparents as myself, is that correct? Thank you very much for your assistance.

          • Yes. In other words, she is possibly your mystery Dad’s younger sister. Or possibly his daughter by a different mother, so your half sister.

  186. Kitty,

    So I just done a sibling test to confirm if my kids are full siblings or not ( They father and other guy are brothers) .. So I got the results today which said the chances of them being full siblings are 52 percent?

    Does this mean they are full siblings or not ? Having the same mum and da do expected it to be alot higher percentage?

    • Jean -I have no experience with commercial sibling tests.
      My expertise is with personal genome tests such as AncestryDNA and 23andme. Because 23andme shows the FIRs, I would recommend that. Then I would be able to tell you whether or not they are full siblings from the comparison of their genomes there. Or if you upload the results from another testing company to GEDmatch.

  187. Thank you so much for your posts on siblings and half-siblings! I sent a glass of wine your way. =)

    My DNA is a horrible mess. People used to joke that we three siblings all came from different fathers and guess what? We did! LOL! My mother swears to God she was working three jobs when I became a fetus and there was no way she’d forget a romp with a strange man, but she’s also 92 and while her mind is pretty sharp that was 60 years ago.

    She fessed up about my sister being from a different father because she got a little suspicious when my sister came down with Grave’s disease earlier in life than you’d expect. She asked my nephew, who at the time was working on his college thesis in DNA, to check hers, my brother’s and my sister’s DNA. She was so sure I belonged to my dad she didn’t bother to ask about mine. She knows now. Heh.

    Bottom line is after seeing your charts and finally getting an autosomal test for my brother, we only share 1,661 cMs, which makes him a half-sibling. Your images in this post really helped me understand how different my brother and I are. Our Chr 1 – 11 look more like your half-sibling example, but Chr 12 – 20 looks like a forest of green lines – none of them form a full-sibling looking block though. The Isogg Wiki sealed the deal with their great cM chart.

    When I ran my brother’s Ancient report, he and my mother’s pie charts looked so much the same, while my Western European Hunter Gatherer was split in half with “American Indian.” I guess I’ll never know who my father is as most of the people who have strong matches with me come from my very strong maternal Hubbard/Byrd ancestors, but I can’t tell you how much I appreciate being able to find this particular information on siblings on the web. I lived my whole life with people looking down at me because I didn’t look like either my brother or my sister and it’s comforting to know the truth about why. =)

    • You are welcome.
      You CAN figure out who your bio dad is from your DNA matches, especially since your brother is tested so you can look through the trees of the matches he does not share with you. If he is from a population under represented among DNA testers it can be harder.
      I recently did an unknown parentage talk at Jamboree, slides are here: https://slides.com/kittycooper/using-dna-for-adoption-searches-27-33-39#/
      Also I have a page for adoptees, the same methodology will work for you see https://blog.kittycooper.com/dna-basics/help-for-adoptees/

      • Thanks for the reply and the links!

        At the moment, we’re trying to solidify that my brother is, in fact, not a full sibling. My mother is concerned, not in a defensive way but from a “I was there, I don’t understand how it could have happened.” LOL! I’m confused about the the 46% HIRs between my brother and I which some say the commercial DNA kit providers would consider a full sibling. My paternal cousin has been gracious enough to give me his raw DNA data from Ancestry to see if he comes up between 400 and 850 cMs with me.

        This has all been very confusing because my DNA matched a 2nd cousin on my father’s maternal side (33.9 cMs). If my brother is not a full sibling, then I shouldn’t match this person. I looked through their family tree for surnames from my maternal side, but there were none.

        The last factor in all this mess is I was born with erythroblastosis fetalis, which for those who don’t know means my mother’s blood was killing me due to her Rh- factor and my Rh+ blood. This was way back 1959 and the “blood exchange” treatment was considered new. It was so new, there happened to be a doctor at Washington Hospital Center that week training people on it and my mother says it’s the only reason I lived as I was severely jaundiced at birth and had I not been premature my mother was told I would have been stillborn.

        I have been told by today’s medical professionals that DNA cannot be altered unless either bone marrow or stem cells are involved. I can’t imagine someone being innovative enough to have taken exchange blood from a donor placenta in 1959 and no bone marrow was involved, but they did have a port in my umbilical cord with which they facilitated two full blood exchanges on two different days; the first at my birth and the second two days later. My mother swears those blood exchanges affected my DNA, but medical science doesn’t seem to support her theory. She’s launched an investigation into trying to find my medical records from my birth to see if there were notes regarding where the replacement blood came from since the person teaching the modality used it on me while he was there.

        In two days I’ll know the results of my cousin’s DNA and mine. I’m not sure what having 1,657 cMs with my brother means if my cousin’s DNA confirms my father as my father. If you were to look at my Ancient Admixture against my mother and brother’s, it makes no sense. My mother has 2.7% American Indian, my brother .27% American Indian. I have a whopping 29.64% American Indian. I’ve heard of recombination, but 29.64%? That doesn’t seem realistic. (My “current” ethnicity breakdown supports the Ancient Admixture results, but I’m told current ethnicity isn’t a solid element to factor in.)

        My raw DNA came from 23 and Me, while my brother’s came from FamilyTreeDNA. To counter any misgivings between the two companies, I’ve taken advantage of the father’s day sale at FTDNA and have purchased a Family Finder kit from them. My mother has an mtDNA kit being processed with FTDNA right now so if my brother’s cMs are coming in 1,000 cMs low due to incompatibilities between the two companies, we will clarify it that way.

        Thanks for all the work you do to help us understand DNA. When I first looked at GEDMatch, I thought for sure I’d never be able to comprehend any of it. Now it actually makes sense. Sorry this reply was so long, but I just want to make sure I didn’t misrepresent the full situation. If you ever find yourself involved in studying something that could benefit from these odd DNA parameters, I would be more than happy to share the kit numbers with you. – J

        • Joanne –
          If you do not share any FIRs with your brother then you are not full siblings. Those can be seen at gedmatch as described in this article.
          There is no biological basis for your mother’s theory.
          Ethnicity is not as adavanced a science as DNA matching for relatives but 29% is significant.
          It i possible that your bio dad is related to you paternal grandmother causing that match. 33.9 is way too low for 2nd cousin.

          • You are correct Kitty!

            I just got the GEDmatch One To One comparison results and my dear cousin and I share NOTHING. Not one half of even one SNP. He and my brother, however, are thick as thieves DNA-wise.

            I feel so anchorless. It’s an odd feeling. Good thing I’m old. Now that it’s really in my face in black and white I guess I’m in a lot more shock about it then I expected to be. Oh well…

          • Joanne,
            Take a deep breath. The father who loved and raised you is still your dad and your anchor, whoever your birth father may have been.
            Many people seek professional help after a shock like this. It is really OK to do that.

  188. Hello Kitty,

    I have a sister, who recently we believed to be my half sister because she had a DNA sibling test done with a family friend whom we thought might be her half brother. The test was conclusive that they are siblings, same father different mothers. So I believed my sister to be in fact my half sister, same mother different fathers. However, I recently noticed in MyHeritage that my sister is still shown as my sister:

    Estimated relationship
    DNA Match quality?
    36.1% (2,556.7‎ cM)
    Shared DNA
    Shared segments
    181‎ cM
    Largest segment

    Is this conclusive that she is my sister?
    And then it is possible that I have a different father than I believed?

    My sister and I have different complexion and hair, and our ethnicity reports are kind of different.


    • Bob
      Those numbers say that she is your full sister. Ethnicity can vary greatly amoung siblings, as can hair color and complexion.

      So yes, either the test your sister had done was wrong or you have a different father than you thought. Get a paternal side cousin to test and see if you match as expected. Use this calculator to check the numbers

      • Hi, another quick question.

        I’m still in the process of verifying the DNA test between my sister and the other person. I believe they had a stand-alone test for that but have since also done MyHeritage. So all 4 of us are in MyHeritage. However, the other person isn’t showing up as a match in MyHeritage that I can find anywhere. I’m trying to obtain the raw download so I can upload it to gedmatch. No progress yet. If I could get a copy of the stand-alone Test they did, would it be reliable? I read that tests like MyHeritage are supposed to be better. Could the stand-alone Test give a false positive. They’ve told me the test says something like 96% possible of … I’ve never seen it so I don’t know the details. Basically I want conclusive proof so I can move forward. Thoughts?

        • Yes tests like MyHeritage are far more accurate for close relationships because they test many many more markers. If you can get all 4 tests on GEDmatch that would make it easy to resolve these issues.

          • Thanks again for the info. On an emotional rollercoaster right now…

            Currently working on gedmatch.

            But I also have their report from:

            Biogene DNA

            It says:

            Probability of Half Siblings versus No Relation: 94.3110%
            Combined Relationship Index: 16.6

            That seems pretty persuasive, but I’m still doing the gedmatch comparisons…

    • This is what I’m getting from gedmatch:

      GEDmatch® Genesis One-to-one
      Autosomal Comparison

      Largest segment = 151.8 cM
      Total Half-Match segments (HIR) = 3557.2 cM (99.185 Pct)
      Estimated number of generations to MRCA = 1.0
      48 shared segments found for this comparison.
      624318 SNPs used for this comparison.
      68.524 Pct SNPs are full identical

      Largest segment = 151.8 cM
      Total Half-Match segments (HIR) = 3554.9 cM (99.122 Pct)
      Estimated number of generations to MRCA = 1.0
      53 shared segments found for this comparison.
      624405 SNPs used for this comparison.
      68.487 Pct SNPs are full identical

      Largest segment = 109.4 cM
      Total Half-Match segments (HIR) = 2568.3 cM (71.613 Pct)
      Estimated number of generations to MRCA = 1.2
      56 shared segments found for this comparison.
      624621 SNPs used for this comparison.
      75.387 Pct SNPs are full identical

      No shared DNA segments found
      627098 SNPs used for this comparison.

      No shared DNA segments found
      624211 SNPs used for this comparison.

      Yet, the report from Biogene DNA says:
      Probability of Half Siblings versus No Relation: 94.3110%
      Combined Relationship Index: 16.6

      Maybe we were interpreting the Biogene report wrong.

  189. Hello Kitty!

    Sorry to bug you!
    A tad confused by all this.

    This is what it says on the stand-alone report:

    Based on the results of the analysis obtained from the DNA loci listed, the probability of Half-Siblingship is 94.3110% (in other words, 16.6 times more likely to be Half Siblings than Not Related). This probability is calculated by comparing to an untested, unrelated, random individual of the Other population (assumes prior probability equals 0.50).

    Trying to understand the discrepancy.


    (again sorry if I’m being a pain in the butt)

  190. I am not an expert on Biogene but my understanding is that you need 99% or close to that.
    So yes you likely misinterpreted it. My heritage and Gedmatch are much more reliable

    • So the info above:
      June 11, 2019 at 8:10 pm

      makes complete sense to you?

      Looks like the friend has zero shared DNA.
      The Biogene people had them believing they are half-siblings.

      This statement appears to be very strongly stating that they are half-siblings:

      “Based on the results of the analysis obtained from the DNA loci listed, the probability of Half-Siblingship is 94.3110% (in other words, 16.6 times more likely to be Half Siblings than Not Related). This probability is calculated by comparing to an untested, unrelated, random individual of the Other population (assumes prior probability equals 0.50).”

      I don’t git it.

      Still confused. If this is true. The Biogene report is totally misleading. Their site says 100% reliable.

      Emotional rollercoaster heading for the exit…

  191. Just found out I have a cousin we never knew about thanks to dna testing. However , I just got my results back and our comparison is in the grey area between 1st cousins and half siblings. My sister is getting tested so that should solve the mystery but is there any thoughts on which this would be ?

    Largest segment = 107.5 cM

    Total Half-Match segments (HIR) = 1335.6 cM (37.242 Pct)
    Estimated number of generations to MRCA = 1.7

    45 shared segments found for this comparison.

    410908 SNPs used for this comparison.

    57.392 Pct SNPs are full identical

  192. I want to know if my sister and I are full sibs or if there is room for another answer. Our Mom is deceased and is the only one who could really shed light on the situation. Ancestry and MyHeritage does have us listed as Full Siblings but there is a huge gap. Ancestry 2553cm and MyHeritage 2409cm. Is this normal for anyone else?

  193. Hi Ms. Kitty,
    I’m in adilemma, as my spouse bought me a AncestryDNA kit and I left it alone because I had so many questions about DNA. There really are no laws protecting the people who get their DNA tested. Long story short, hubby kept asking over the next yr. when was I going to take the test. So I took the beaker and spit in it and forgot about. Until I was contacted by a young lady. She did Ancestry DNA and she gave me the results. We have ⁰1618 cm across 72 segments. Am I her Aunt? I’m very confused. Also a guy contacted me, as he said he has been working on his dad’s DNA, also from Ancestry. His dad and I have
    270 cm but I don’t know the segments right now. However, I can get that info. What is the relationship between his dad and I? I can’t explain how confused I am. This guy, who’s doing his dad’s line came up with these; he believes my great grandmother got pregnant by a 15 y.o. boy, who was a Manning. I went through the 10 generations my hubby did for me on both sides of my family. That was difficult, as my mom was from Holland. Anyway, I told this guy that I felt he was far reaching. My family were very old and still making babies. I have my great grandfather’s military records, as he was in the Civil War. I couldn’t find any Manning in the paternal side, except for some other names that we share in common, as in Apgars and Alpaughs. I next told him I felt our relationship occured around my great, great, great, great, great grandfather, as there were marriages between the Tigers and the Mannings but I don’t know exactly how we are related since I couldn’t find any Mannins but did say I didn’t have the names of the wife’s family, so it could be we are related that way. I just know we aren’t related because of my great grandmother had sex with a 14 y.o. boy with the last name of Manning. Please help me, as this has caused some trouble with my last two living sins. I apologize this was so long but I need someone to straighten me out. I have already accepted this young lady as myneice. Thank You for all your help! Sincerely, Martha Tiger-Ochs

    • I replied to your other post. Out of wedlock situations are not usually well documented so there would be no Manning in your tree, but we can figure them out from the DNA.
      Here is my slideshow on figuring out unknown parentage situations.
      To see the actual segments you need to upload elsewhere but ancestry will show you the number of cMs and segments on your match list page.

      He is your close relative, about a 2nd cousin

  194. We are trying to decipher some results……several family members did the Ancestry DNA test (all female). My DNA Matches show my two nieces (who are my age) as “Full Siblings” with 2,161 cM and 2,120 cM shared. It shows my two sisters (one is their mother-confirmed) who are much older than me, as well as another unknown individual, as “Close Family” with 1,854, 1,601, and then 1,755 cM shared.
    We are all confused! My parents have passed away so we are trying to figure out how accurate the “Full Sibling” and “Close Family” tag is? Is it accurate that my “nieces” are really my sisters? Why are my “sisters” only showing as close family?

    • DJ –
      It sounds like there was an in family adoption. The numbers fit with you being the niece of your sisters and the half sibling of your nieces. In other words would it be possible for the mother of your nieces to have had you when she was very young and your grandparents adopted you … It could be more complicated than that.
      What I would recommend is all of you upload to GEDmatch.com (please opt in to help law enforcement) and look there at the X comparisons and the HIRs and FIRs (see https://blog.kittycooper.com/2019/10/why-dont-we-share-more-dna-with-a-sibling ).

  195. Hi Ms Kitty,
    My half-sister and I share 1980cM across 70 segments (on Gedmatch this appears to be 2171cM across 91.5 segments). Could these numbers tell us whether our fathers were related?
    Is there a way we can find out if our fathers were related through Gedmatch with both our kits only?
    Much appreciated.

    • Hi Roselyne –
      The way to tell if your fathers are related is to look and see if you have any FIRs (Fully Identical Regions) in your DNA. You can see that by looking for green bars in the image or by checking the box “Show only Full-Match (FIR) segments. ” in the one to one comparison. Do also check your X for those green bars.

  196. Hi Kitty,
    I have grown up with all half-siblings, some from my mother’s prior marriage and some from my father’s prior marriage. I found one of my half brothers (12 years older than me) on my mothers side as a DNA Match on AncestryDNA. It matches me to him however as a full sibling (2,775 cM across 65 segments). It also shows a number of ‘shared matches’ of cousins and an aunt on my father’s side of my family. Before I discuss this with him, do you know if there is any possible way that this could be wrong?

  197. Hello,

    I wanted to find out if there is a definitive way to tell what a relationship is when it says 100% grandparent/grandchild/half sibling/aunt/uncle. I have DNA tested myself and my mothers sister and my sibling and a known 1st cousin on my mothers side.

    However, after taking the tests, I show that a “close family – 1/2 sibling – 1st cousin” match shows up, quite unexpectedly. Both of my parents have passed, so I cannot get a DNA sample from them.

    The cM range for me between Ancestry, 23andMe, MyHertiage, FamilyTreeDNA, and GedMatch, are 1663.9cM and 1809.4cM.

    The cM range for my sibling ranges from 1514.9cM and 1585.8cM.

    First, from what I understand, the cM’s are so high, it is almost definitively a 1/2 sibling vs. a 1st Cousin. Am I correct in that thought?

    Second, for this match to be an aunt or uncle, it would have to be a full aunt or uncle vs a 1/2 aunt or uncle. (And would it be considered a 1/2 aunt/uncle if they were the child of my paternal grandfather?) Am I correct in that thought? This person is 12 years my junior, so I’m still leaning towards 1/2 sibling, although a 1/2 aunt or uncle is not out of the realm of possibilities – except when you look at the number of cM’s.

    Also, would race be a factor in the strength of cM’s? I’m highly doubtful in that.

    What I’m trying to figure out, through all the DNA resources I have, is this…. Could this person be a product of my paternal grandfather and this persons mother, or could it be a product of my father and this persons mother? Or, could this person be a product of my fathers brother and this persons mother? What would be the cM range for all of those?

    Thank you.

  198. CH,
    You left out the possibility of niece/nephew, how much is shared with your sibling? I presume there is no match with your mother’s sister?
    The cM are too high for your grandad to be the father ( half aunt/uncle) and your fathers brother would make this person your first cousin and again too high.
    Since you are both at Gedmatch, use this technique to perhaps figure it out

  199. Me and my half/whole? brother share 2450cms across 70 segments..twist in the story..my fathers son from another marriage may be my dad…yes my mom had been with the father and son.. would the father and son make it look like we are whole when maybe we are half??

  200. Hi Kitty, my sister and I share 2,781 cM over 53 segments (largest segment 223 cM). We have fully identical segments (FIR) on all chromosomes but the X (where we only had a small portion of half-identical segments).

    Are we full siblings or half siblings? And why don’t we have any fully identical segments on the X chromosome? Is it because I’m male and she’s female or is it something else I’m not aware of?

  201. You are full siblings with so much shared DNA, see today’s post about the calculator. As to X, being male you have only one X so would not have any FIRs on the X with anyone since that requires two chromosomes with identical DNA at those positions.

  202. Good morning, I have a Dna Match Total Half-Match segments (HIR) = 1061.8 cM (29.632 Pct)
    Estimated number of generations to MRCA = 1.9
    Largest segment = 80.3 cM
    Is this match possible to me 1/2 sibling? what additional testing would confirm finding?

  203. My sister and I both took the Ancestry DNA test, as did my daughter. My sister and I only share 1864 cM over 48 segments with the longest segment being 107 cM. Neither my daughter nor I share any relatives on my father’s side of the family with her according to Ancestry, only on my mother’s side. Charts suggest she is a half sibling at nearly 100% accuracy. When asked about her results, she just said she thinks it is all just made up stuff. Our mother is alive at 92, but not approachable, either. Are these percentages accurate? Is there another scenario to consider?

  204. Elaine –
    Hugs, sorry if this is difficult. She is your half sister. Given that you do not match anyone on your father’s side of the family, you have a different biological father from your sister.
    DNA does not lie. Close relationships based on shared cM are accurate although sometimes there are alternate explanations (aunt/niece look like half sisters) but I do not see that possibility here from what you said.
    The only made up stuff is sometimes the smaller (think 1%) ethnicity calculations but these are getting better all the time

    • Thanks, Kitty. I and my daughter share both my dad’s and my moms relatives through Ancestry. My sister only shares my mom’s relatives when my daughter and I compare our matches. I suspected and figured my Dad was not her Dad. She is the youngest of us 4, and only the 2 of us are alive. She will always be my sister, so unless she brings it up, there is no reason to stir the family pot at our ages.

      • In my opinion, truth is the correct policy. Holding a secret can be toxic and it may come out other ways and then how will she feel that you kept this from her? Also your sister may have other family out there, other half siblings and so forth.
        But you know her and your family best.

  205. Hi Kitty
    I’m wondering if you can clear something up. My daughter did a dna test and she came back with someone as 1st cousin once removed – 2nd cousin 322.1cm. I believe her to be the Grandaughter of my father how ever her mother and i would be half siblings as we don’t share the same mother. If this is correct i’m trying to understand why it would comeback as once removed and not just cousin