Size Matters for Matching DNA Segments

The more large segments you share, the more closely related you are to a DNA match. To learn more about segments, read the new blog by one of my favorite DNA writers on the yahoo DNA-NEWBIE list, Jim Bartlett, called
Brynne Ancestor MapHe explains why you share such large chunks of DNA with your closer relatives by showing how recombination works and how few cross-overs there usually are in a recent post at

While the total amount of shared DNA in centimorgans (cMs) is a fine indicator for your closest relatives out to second cousins, farther relationships can be more and more random in the amount of shared DNA. You can consult the charts and numbers at ISOGG here – – to determine those closer relatives.

Although I like this new chart from Blaine Bettinger the best:

Shared DNA statistics from Blaine Bettinger

Shared DNA statistics from Blaine Bettinger, used by permission

Note that since you share about 25% with an aunt, uncle, grandparent, grandchild or half sibling the amount shared cannot tell those relatives apart [UPDATE 20 Oct 2017: See my study results showing that paternal half siblings can be told from the others here ]. Sometimes the X can help distinguish those, see my post on that here.

Frankly the testing companies are not that accurate in predicting your more distant relationships, those past 2nd cousins. So when deciding which DNA matches to pursue, follow up on the ones with more than one large segment; those are your closer relatives, the ones whose trees may be easier to connect to yours.

122 thoughts on “Size Matters for Matching DNA Segments

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  1. With my two successful matches, or matches with whom I found a connection, I know how unpredictable the size can be. And recently, after having a lot of cousins tested and two of them are 2nd cousins to each other and they share the largest segment 40.4cM, total 157cM, to me was a good indicator on what 2nd cousins should be sharing, more or less. Since I get pages and pages of 2nd cousins, if not predicted closer (FTDNA), it was good to go by this.

    My mother has had a 50cM largest segment match (total 122cM) and knew that this had to have been a close match. Took me over 7 months to figure that out (actually 11 straight days of non-stop research) to find out that my mother and this match are 1/2 third cousins. Pretty distant in a way, but that 50cM is pretty large. The next largest segment is 38cM.

    My mother gave my brother basically that same largest segment whereas I got only 14cM of that same exact segment. I actually share 28cM of that 2nd largest segment, but had I not got my mother DNA tested (I tested first) I wouldn’t have paid attention to that match, and actually I didn’t until almost a year after my mother tested.

    Definitely from 2nd cousins on it can be unpredictable.

  2. Kitty, a great post – and thanks for the plug. My true brother and I have such a mish-mash of DNA, that the Admixture/Ethnicity programs look like we are not related! DNA is random and very variable.

  3. Kitty – Great post. I’m so glad you like the chart! I’m still working on the Shared cM Project, there’s so much still to do, stay tuned!

    And I agree, Jim’s blog must be added to everyone’s must-read list!

  4. Hi Kitty,

    I am trying to understand the significance between “Total Segments” and “Largest Segments” on Gedmatch. If you have let’s say, 8 matching segments with someone, and the largest segment is maybe 4 or 5cM, and the total of all segments is maybe 17cM, is that of significance when trying to find a common ancestor down the line? I guess I’m confused with terminology because I keep reading in many places that matches over 10cM are pretty good ones, but I don’t know if this means 10cm on one segment alone or a total of multiple segments.

    • Reg,
      In your example the segments are too small for the relationship to likely be findable.
      If there is no endogamy in your tree then anyone who matches you on multiple segments of 7cM or larger is worth following up on. Segments smaller than that are often false, below 5cM they are false more often than true.
      Use total cM of 7cM and larger segments with the charts above which you can get on the one to one compare

  5. I am more or less the kit Admin for my adopted Japanese daughter in law. I noticed two of her matches, a mother and daughter have a lot of small segments. The mother daughter pair are probably 3c1r and 4th cousin. The daughter has the most looking at 3cm she has 130 cM total, other 4th cousins have maybe 30 to 40 cM some a little more. Does this mean anything? I was thinking maybe they are a little closer than they appear?

    • Alan –
      Small segments can be population specific. We tend to only look at matching segments greater than 7cM and total those. Also large segments greater than 20cM are indicative of a closer relationship not lots of little segments.
      Look at the numbers here after you total the larger segments.
      Also if the daughter has matching segments that the mother does not, they would come from her father. Matching on both sides like that can make a relationship look closer than it is.

      • Hi MsKitty,

        Love all of your data, i am just getting my 23andme results back and trying to reach out to some of my “Closest” cousins haha. I am talking to one that i match two segments on the X chromosome at 22CM and 9CM i assume i should definitely pursue research there right? I mean we only share .45% DNA, but having two over 7CM on the same Chromosome matters right? SOrry, i am new

  6. i share546 centimorgans shared across 24 DNA segments with a match …
    trying to figure out the relationship ..she said its her moms side of the family and she is the half sister and her brother gave a baby girl up for adoption ??

    • Deanna – I am not sure what you are asking. That is on the low side, but the DNA match could be a half-niece relationship. If you are an adoptee or she is, then I recommend the web site plus join their mailing list at yahoo and ask questions there. Or DNA detectives on facebook.

  7. Hi Kitty,

    My Mom shares 89.8, 3 segments (chr 1,18,21) longest 74.4 (chr 1) with a male match and
    she also shares 187.2, 6 segments (chr 5,6,7,9,14), longest 78.4 (chr 9) and (chr 14 at 41.5 and 15.3) plus 26 “X” cMs with another male match. Any significance in 2 long segments within one chr?

    I’ve found the same MRCA in their trees but they don’t match each other on Ancestry or Gedmatch! It’s like they’re not related to each other (and not in common with my Mom) but I know they share this Hood line. Can you share any wisdom on this issue and both having long segment matches with Mom? Both are in their 60’s and Mom is in her 80’s…

    Mom’s 187 match thinks it’s possible his great Uncle or a 1/2 great Uncle may be my Mom’s great grandfather. Which means they would share a 2nd great grandparent. I’m having trouble with this because they share more DNA than 3rd cousin level? Thank you!

    • Debbie
      My apologies, I seem to have missed your comment. How long ago do they share the Hood line. A few 3rd cousins do not match at all (10%) and about half of 4th cousins do not match. See

      And that is a fine amount for 3rd cousins to share. Blaine’s latest chart shows average 79cM and range 0 – 189

      The amount of DNA shared past 2nd cousins gets more and more random …

  8. Hi Kitty, I am trying to find my Ashkenazi father. This is one of my closest matches from his side from Gedmatch. Any insight on what type of relationship this is with the endogamous component. Trying to decide if it is worth proceeding with, what do you think? Thank you so much for considering.

    Minimum threshold size to be included in total = 500 SNPs
    Mismatch-bunching Limit = 250 SNPs
    Minimum segment cM to be included in total = 7.0 cM
    Chr Start Location End Location Centimorgans (cM) SNPs
    1 242,426,244 245,689,563 8.9 634
    3 5,828,299 71,791,127 78.9 10,022
    6 6,813,583 10,288,551 7.1 588
    16 60,358,369 76,240,659 12.9 1,896
    Largest segment = 78.9 cM
    Total of segments > 7 cM = 107.8 cM
    4 matching segments
    Estimated number of generations to MRCA = 3.5
    397067 SNPs used for this comparison.

    • Definitely worth pursing that match, about a 3rd cousin, 2C1R, 3C1R, 4th …. the large segment is promising for a closer match.

      See Lara Diamond’s family statistics for an idea of what endogamy does to shared cMs in relationships past 2nd cousins:

      My new rule of thumb for DNA cousins past 2nd on the AJ side which meet the one segment > 20 and another > 10 criteria is to halve the total cMs and then look that number up on the chart …

    • Sorry Wendy, I seem to have missed your comment. a large segment like that is usually closer family 3rd cousin or closer but it is the total cM which we use to estimate the relationship as in the chart shown above.

  9. Hi, i cannot find the segment lengths from my testing company. I surprisingly matched to several members of a family I do not know. They range from less than 400 cM to around 175cM, over 12 but under 20 segments. Is there any way that this possibly is IBS? I did this for med info and ethnicity for fun, this matching was a total shock. Please advise.

    BTW, Do you do consults? Kind of…..bowled over.

  10. Thank you for your article. It has been one of the most helpful in trying to understand smaller segments and their possible significance or non-significance.
    I understand that if there are a small number of matching segments, there is little chance of relationship.
    If there is a segment that is over 7 cMs and it is accompanied by a small number of matching segments, it may or may not support the indication of relationship.
    My question is, because I have a number of matches where this is true, I will have a match with someone where the total of matching segments (using the 7 cM default) is over 25 cMs, even up to 60, and those matches are accompanied by a large number of segments (20 to 30) which are smaller giving a total number of shared cMs between 60 and 100.
    Do those smaller segments support the relationship?
    Do they indicate a closer relationship?
    Does paying attention to the chromosome where the segments are found help to understand? (For example, on the 8th chromosome there are 5 segments which add up to 12 cMs)?
    Thank you for taking the time to answer.

  11. My advice is to ignore most of the smaller segments below 7cM and use the total of the larger segments with the chart to make a guesstimate of the relationship.

    Sometimes the 6s and even the 5s can be valid and triangulate with other relatives but for the most part they are false.

    Having many of the smaller segments will often occur when you are from the same population group so likely you have shared ancestors many hundreds of years ago, further back than the records. That is all a plethora of small segments might indicate. Not relevant to the closeness of your relationship.

  12. Hi
    I have tested with several DNA companies & my closest match on my Ashkenazi side is on MyHeritage. The match is:Shared DNA 1.7% (125.2 cM)
    Shared segments 4
    Largest segment 82.8 cM Is This a match worth contacting etc. I am an adoptee searching for my birthfather.

  13. I am reposting an issue of mine, to get an expert opinion (analysis) from someone on this Blog who maybe an expert on small segments. I’ve read there is a lot of debate on the topic and is usually negative. I’ve read ISOGG and Blaine Bettinger’s blog and others. There is an issue, where on a surname line came from the same small town as my same surname line came from. I really thought we were related as 4th to 5th cousins. Ancestry match results bottom’s out at 6 cM. With the background on my line, some of the matches with my surname, I would say the cM’s shared were really low in that my grandfather and my great-great grandfather did not pass much shared DNA down to me according to a chart, ‘DNA Detectives Autosomal Statistics Chart’ and other online statistics charts. I was wondering to myself, how would I match to 4th to 5th cousins, or have the same common 4x great grandparents.
    So I uploaded the results to GedMatch which you can lower the Centimorgans to 3. I compared myself to the other line with start to end as follows: 23,278,836 to 28,530,339, 4.5 cM, 900 SNPs on Chr.5 and 27,093,528 to 47,702,256, 5.0 cM, 1,220 SNPs on Chr. 16. I compared myself to the other line’s Aunt with start to end: 23,568,400 to 28,355,305, 4.2 cM, 823 SNPs on Chr. 5 and 27,273,899 to 47,576,695, 4.4 cM, 1,126 SNP’s on Chr.16.
    I checked my niece’s kit to the other line realizing that she would be a generation offset(more distant) and this dropped the Chr. 5 results. I compared her to the other line with start to end as follows: 27,729,894 to 47,573,693, 3.5 cM, 1,021 SNP’s. I compared her to the other line’s Aunt with start to end as follows: 27,729,894 to 47,573,693, 3.5 cM, 1,015 SNP’s on Chr.16
    All three of us have common, somewhat overlapping segments on Chr. 5 and 16 with somewhat strong SNP’s, with at least 4 cM not 3cM’s. Even my niece’s less than 4 cM’s results, hung in there with Chr.16 with rather large SNP’s. In some study on small segments that quote, “When utilizing small segments, I generally don’t drop the SNP threshold below 500”. SNPs are larger than 500.
    My ancestor did change his first name when he came to America on the boat, but there are documents such as parish/church records from here and in Germany. Why he changed his name, not sure why, but it could be a confirmation name which are not documented in parish records in Germany.
    Would you think that my line and the other line with the same surname are related (Identical by Descent)?

  14. This is way too complicated for a quick answer on my blog but yes this could be valid, especially with a large number of SNPs. Test more cousins on each line to try to confirm. Oldest generations best.

    Small matches in cM of 4-6 with high SNPs are possibly valid if they triangulate but beware, these can also be population segments. Look at who else matches you there.

  15. This seems high for a 2nd cousin. I know who it is, we thought we were 1/2 first cousins. Isn’t this more within a 1st cousin range? Thanks!

    Chr Start Location End Location Centimorgans (cM) SNPs
    1 59,215,941 120,075,978 59.4 6,288
    1 179,426,082 194,391,631 11.9 1,085
    2 42,188,689 74,825,589 33.0 3,734
    2 77,198,999 119,936,267 27.8 2,853
    3 38,411 28,993,092 51.8 4,120
    3 128,952,856 157,910,521 30.3 2,676
    3 185,884,816 196,259,734 26.1 1,422
    8 30,337,787 68,738,971 25.8 2,556
    9 5,686,021 33,398,019 43.0 4,039
    9 71,030,216 79,391,121 9.2 1,007
    11 10,373,830 107,128,834 91.8 9,180
    13 35,350,141 111,813,664 92.5 8,150
    15 67,889,745 98,108,585 52.3 3,753
    20 24,474,724 53,492,826 33.5 2,768
    22 14,884,399 24,620,588 25.9 1,091
    22 25,392,038 49,524,956 50.4 3,300
    Largest segment = 92.5 cM
    Total of segments > 7 cM = 664.6 cM
    16 matching segments
    Estimated number of generations to MRCA = 2.2

    • That looks fine for half first cousins, a little on the high side but DNA is pretty variable. It could also be full first cousins as you suggest. Another possibility is that the parents who are not expected to be the same are related. Any endogamy in that tree?

      You can confirm the full versus half by testing 2nd or 3rd cousins or other close relatives that you expect NOT to be related to both of you. If they are only related to the expected person, that would confirm the halfness. If they are related to both, but very unequally, it could be the related issue. So you may need to test even more people.

  16. Hi,

    My Mum has a match from another country with an SNP of 627 and 8.6 cM. It states around 6.8 Generations. Is this a positive match? This match would mean us. Thank you:)

  17. Awesome. Thanks so much. Its pretty exciting to me. My ancestors were traded, so having a match from the continent is very amazing. I understand it will be very distant though. I will be testing much older relatives to see if they have the same match too.

  18. Four of us sharing a very rare Irish surname amongst known ancestors have been lucky enough to separately stumble upon each other during Internet searches during the past several years. From family histories and records, we all knew we had rare surname ancestors coming from the same small area in County Mayo, Ireland dating to early through mid-1800’s. Based solely on family histories, we wondered if all four of us might have the same great-great-great grandparents or great-great-great uncles/aunts. This month, we all posted our DNA test results at GEDmatch to see how or if we match. The results are a mixed bag. For one person (I’ll call “Judy”) for whom I suspected (before DNA testing and from family history) her known great-great-grandparents might also be my “lost” great-great-grandparents, the GEDmatch 3D Browser showed that she and I matched on 14 different chromosomes and a total of 27 segments, for a total shared cM of 77.5. However, all 27 segment values are on the low side, with the highest being 5.2 cM. The others were: 3 segments between 4.0 and 4.9, 17 segments between 3.0 and 3.9, and the rest less than 3.0. So, lots of Crs, segments, and total cM but very modest segment values. For this same “Judy” person, another one of the four of us showed a match at or above 3.0 on only 8 different chromosomes and 9 segments, totaling to 35.0 cM but with the highest segment at 9.1. So, a higher highest value than mine….but on much fewer Cr’s and segments. Does the fact that I match on many more Cr’s and segments, but with a lower highest value on a single segment (5.2 cM vs. 9.1 cM) imply any greater probability of a 5 or 6 generation common ancestry to “Judy”?

  19. Matches below 7cM are often false which is why we look at the total of segments > 7cM. Your matches are too small to be conclusive.

    For a rare surname the best strategy is to test the Y of the men with that surname, at least 37 markers. At family tree DNA (use my link in the footer so I get a little credit). This reaches back many hundreds of years, much further than autosomal which is not guaranteed to produce matches beyond 3rd cousins ….

  20. I have a niece who tested at both and MyHeritage. The results came back 880 centimorgans and 50 segments on but 403 centimorgans and eleven segments on MyHeritage. What will be her predicted relation to me(uncle). Thanks in advance for your reply

  21. The ancestry result suggests she is a half niece, that is to say her parent that is your sibling is likely a half sibling.

    Does she match relatives on just your maternal or paternal side? Test a few cousins …

    So did either of you actually test at MyHeritage or did you upload your results from ancestry? The same company and chip? I would contact customer support at MyHeritage as that seems too large a difference.

  22. mskitty I uploaded my data from ancesterydna to MyHeritage, my niece match relatives on my maternal side of the family. I am assuming her father and I are half sibling. My brother is having a hard time with this since I am name after our father. Who is decease. Thank you for your reply!

  23. Thanks Kitty, your comments and reply has been quite helpful! I will read – The Stranger in My Genes by Bill Griffeth.

  24. Hi Kitty,

    Our family is trying to solve a brick wall. I am using the Blaine T. Bettinger chart which was updated March 20, 2017, and goes out to 8C.

    Cindi (my 1C1R) and I have both tested with Ancestry. We both match Tina, me at 56.7 cM over 1 DNA segment, and Cindi at 37.8 cM over 1 DNA segment. Using the Bettinger chart, I figure that Tina is my 4C1R, because it seems that we share too much DNA for it to be a relationship which is further away. Notably, my sister Kim has 0 DNA in common with Tina.

    It seems to me that 56.7 cM is a fairly large chunk of DNA, but I don’t understand the implications of it being over 1 segment, as opposed to, for example, 3.

    I welcome your insights and suggestions

  25. Hi Kitty! I hope you can answer this for me! I was adopted and recently did a DNA test on Ancestry, many surprises in my ethnic background, however I am more curious about a match who came up as a first cousin, I am thinking she may be my half-niece. We share 947 centimorgans over 45 DNA segments. Her sister, who has a different father than her had a lower match 639 centimorgans over 32 DNA segments. Is this at all possible? I ask about the niece match because her uncle and I have spoken often and his father matches almost exact what I was told about my bio dad and the ethnicity matches as well. Thanks in advance for your help!

  26. Hi-
    I’m just starting with all this, and it’s like learning a whole new language! I’m sorry if my questions seem rather simple. I tested with 23andMe, uploaded to all the usual spots. I’ve got my Ancestry test pending. Trying to find biological family.

    So, when I look at these comparisons, what is the most important thing to be looking for, length of segments or number of segments? I have one who we share 36 cM on one, with 2 other, smaller segments. Also, I’ve found 2 other people who share almost the identical segments with me and the first person. Would that indicate that the 4 of us share a common ancestor?

    Also, I have another person who shares 46.6cM on a different chromosome, but only that one segment.

    Are any of these significant? Thanks for any help you can give.

  27. Great article! I have a known second cousin who tested at FTDNA. We did not match, but he matched my grandmother who is his dad’s first cousin. When I uploaded our results to gedmatch, we only matched on one segment at 13cms (he matched my grandmother at about 300cms). The predicted relationship was 5th -8th cousins! I really expected us to have a higher amount of shared DNA because everyone else in my family who tested matched him pretty high. If I didn’t know our MRCA, I would have discounted it as being really distant.

  28. Your information is quite helpful to me, but I am having a problem identifying cm numbers which are relevant for me. My mother was adopted and I am searching for her family. I have tested on both Ancestry and FTDNA and find the cm matching counts to be so different. I have quite a few matches who have also tested on both and the results can vary significantly. They difference can range from 10 cm on Ancestry to 60 cm on FTDNA and other similar differences. When there are not many very high matches for me to pursue, I would like to know which testing company’s results are the most helpful for my purposes. Thanks for your help.

  29. Hello Kitty, I have had a DNA test done by I am very puzzled by one particular relationship result. I share 1485 cms across 50 dna segments with my father’s first cousin, my brother is 1146 cms across 45 dna segments, suggesting (to me) that this is an aunt, not a cousin. My four children range from 747-915 cms across from 28-36 dna segments, suggesting a first cousin. My logic (hopefully wrong) is that my grandparents were siblings. I’m not completely shocked, but saddened as this would go far to explain a family split in the 1930’s. May I ask your opinion? Thank you, Broertje

    • Broetje –
      These are both within the range for a first cousin to you two but too high for a first cousin once removed which is what your father’s cousin would be. Could this cousin’s parent be your father’s sibling? A within family adoption? Are any of your father’s generation alive and willing to test?
      Only more testing can resolve this. You might also layout a McGuire diagram. If other cousins are tested, are they getting similar results? No I would not leap to your conclusion yet


      • Kitty, thank you for your very helpful reply. This cousin of my dad’s has a brother and sister still living, but I’m not sure if I can convince them to do a test…..I might have more luck with her son. I haven’t even considered telling them that their much loved father might have done the unthinkable, even if I was absolutely certain. There are no others left of that generation. I don’t believe she was dad’s sister, she’s the middle child of my great uncle and his wife, and he and my grandmother and their sister were no longer on speaking terms by then. Sorry about all the details, but I am trying to be very thorough. I did suspect this a while ago and the DNA results are beginning to look like confirmation. I appreciate your help, it’s a relief to be able to ask an expert questions.

  30. Hi
    My mum shares 342 cM over 13 segments with a man only on Ancestry who won’t share their tree – help ! * and with a great grandfather to find we think it is THAT crucial line. What to do ?! Could his great grandfather or great uncle, or grandfather or uncle be my mums grandfather ?

  31. Correction – I meant ” * and with a grandfather (of my mother’s) to discover we think it IS THAT crucial line. What to do ?! Could his great grandfather or great uncle, OR grandfather or uncle be my mum’s grandfather ? All advice very welcomed. The 3 shared matches don’t match each other and are very small cM.

  32. I thought I found my (half) brother’s grandchild. The results show there are only about 545 cm shared between them. I share 632 cm with this child. Is this possible or should I be looking a generation back for answers.

    • If you share more DNA with this person than your half brother then it is almost surely not his grandchild. Any DNA his grandchild has in common with you would be from your half brother unless you are from an endogamous (very intermarried) population. Another possibility would be if that person is somewhat related to your other parent.
      That amount of DNA could certainly be a half great-nephew for the both of you or a first cousin once removed
      Have a look at Blaine’s latest set of charts for the possibilities

  33. Hi Ms kitty, Thanks so much for having this blog.
    I am very new to the world of DNA and adopted with no information on my biological family but I am reading as much as I can. DNAadoption has a lot of good information.
    I did my DNA with FTDNA first then Ancestry. I did upload my data on Gedmatch. On FTDNA my first match I share 104 cM, total cM is 85.78. We have plenty In Common With also.
    Are the numbers I share with my first match a good start or are the numbers on the lower side if I wanted to research the matches we have in common? Hope that all makes sense.

    • Hi Patti
      I really recommend you join the DNAadoption mailing list at Yahoo and/or DNA Detectives at Facebook and ask questions there. Better yet take a class at DNA adoption
      That match is a start but not the 2nd cousin match or better you would hope for, since 106 is only about a 3rd cousin or 2nd once removed. Still with enough of those matches, you can find your biological family but it won’t happen overnight.

  34. Hello Kitty!
    I completed an AncestryDNA test. I shows I have a close relative. We share 1,656 centimorgans across 64 segments. What is your take on what their relation may be to me?

    • Hi. My wife also completed an AncestryDNA test. It shows she shares 1,788 centimorgans across 78 segments with a woman. She contacted the woman and it turns out the woman is adopted with a half-sister. This woman and her half-sister share 1723 centimorgans across 76 segments. Does this mean my wife is most likely a half-sister to this woman?


  35. Hi. I took the Ancestry DNA test and a woman showed up as a 1st-2nd Cousin. Although she’s predicted to be a 2nd Cousin. It says we have 406 centimorgans shared across 25 DNA segments. I don’t know this woman and her alleged parents and grandparents or great-grandparents are not related to me. I’ve have researched my genealogy for over 15 years and her alleged family doesn’t appear anywhere on our tree. What are your thoughts?

  36. Xavier –
    The most likely relationship is 1st cousin once removed or half first cousin or second cousin. There are many possibilities along those lines.
    As to how this could be, she might be adopted and that is her adopted family’s tree. She might not know she is adopted. Or you or she could have an unexpected paternity event (NPE) where one of your grandads or great grandads is not the name on the birth certificate. What is your age difference?
    Start by using Michele’s tip number five to verify all your family lines
    Then contact your new relative and work on this together.

    • Kitty –

      Thank you! And thanks for replying. She and I are the exact same age and she curiously resembles my own mother (I saw a FB photo). Btw, she’s related on my mother’s side of the family. My mother’s FATHER side. I thought perhaps she was one of my mother’s brothers NPE children. Or perhaps even my grandfather’s NPE child. But now that you’ve mentioned once-removed I do wonder if she’s one of my mother’s first cousins’ NPE daughter. She also shows up as an exact 2nd Cousin for my nephew. They have 258 centimorgans shared across 15 DNA segments.

      • She could be any of those things, get some more family members to test whose results will help narrow this down … Cousins, uncles …

  37. Is there anything like this for large X matches. I working on a match that share 138 cM on the X but only about 8 cM autosomal. Any ideas? There is one other match that has 58 cM of the same segment.

    • X matches are much more variable than autosomal matches because the X passes through males without recombination. So no they cannot be predicted.
      Since a small autosomal match is included, my guess would be a 3rd cousin or 3rd once removed.

  38. Kitty, I have a general question for you. My DNA show 100% European and I have some really good matches, many of whom I’ve been able to confirm. My husband has 66% Native American ancestry. I noticed that my closer matches are much lower total cM matches, but larger segments. His closer matches can be MUCH bigger in terms of overall cM, but the segments are usually quite small. Is that something to do with the gene pool? I’m Heinz 57 from many countries and his ancestry from both parents is from a small area in one country.

    • WK –
      Likely his closer looking matches are not as close as the total cMs indicate. If they are all from one area, there could be cousin marriages affecting the amount of shared DNA. Also small segments can be population specific as opposed to recent common relatives.
      Your close family out to about 3rd cousins will share larger chunks. Also do not use the totals from your testing company, best to total all the segments > 7cM yourselves. Anestry totals are OK but upload the data to GEDmatch to see the segment sizes.

      • I wouldn’t trust Ancestry. I used ftdna and then uploaded to gedmatch. I’ll used the >7cM rule on his and see what it looks like. I was pretty sure that the smaller area and possible cousin marriages would affect results, but I wanted an expert opinion. Thanks so much for your blog and for the very fast reply. Much appreciated!

  39. All other things being equal and assuming no endogamy, can you give us a generalization regarding the interpretation of a situation where you have 2 12 cM segments vs a single 24 cm segment? How would chromosome location factor in, e.g 2 locations on same chromosome vs 2 different chromosomes? I am concerned about probability vs “magic thinking”.

    • It is not possible to give much of a generalization because of the randomness of DNA inheritance. I would feel more confident that I could find the relationship to the person with the two segments but often that can be each from a different ancestor so still pretty far back

  40. Glad to hear that. One of my ‘hooks’ to encourage AncestryDNA matches who share multiple segments to post their kit to gedmatch is the possibility of finding two sets of MRCAs for the price of 1 (especially when the shared matches showing in Ancestry are mixed between 2 diff lines – I code all matches based on their matches). But, as the number of shared segments > 7 cM increases, does that not undermine the assumption of independence, statistically speaking, because of proximity and the likelihood they came from the same line generally speaking?

    • Jenny –
      It just depends on how small a population pool those ancestors had as to how likely it is that two segments = two MRCAs. I start with the assumption that it might really be a 4th cousin match or so with one MRCA.

  41. Thank you for taking the time to talk about this while I struggle to ‘debug’ my thinking. Because I come from mostly early colonial era in the US except for one line that got here in 1840, I am very used to seeing my ancestors in random trees all over the place so it wouldn’t surprise me to have 2 sets of MRCAs for 2 segs, but I am struggling with “magic thinking” — always a problem when working with probablilties. I must imagine that the closer the match AOTBE the more likely the segments came from the same line in my tree but with different possible MRCAs in that line but that a couple of smaller segments for a match who shares less cm could have come from 2 different lines and MRCAs as they get further back in time where there are many more degrees of freedom. But, then I imagine that it’s not necessarily as independent in the statistical sense to the degree that the multiple sets of MRCAs are coming from the same area/ Does that make sense? Similarly for the case where the two segments are on the same chromosome.

    • Jenny –
      DNA inheritance is too random past 2nd/3rd cousins to apply much math. Large segments are good and tend to be from more recent ancestors. Single segments are less likely to be findable than two large segments. However as we said, two can be from different lines so just as hard to find.
      When your ancestors intermarried it gets more difficult to figure these out.
      My advice is to start with your closer matches first – I love this slide I did to illustrate that

  42. Kitty, thank you so much for taking time to discuss this with me. Regarding starting with closer matches, I completely agree but on my mom’s kit I’ve solved as many as I knew personally and most who posted to gedmatch or had kits where a chromosome browser was at hand, but since I only had the kit for her, I’ve been testing this approach: made a master spreadsheet of all her matches using gedmatch Matching Segs: then decomposed them in to two groups for every discreet group (no overlap); then based on who was in the segment, classified them as maternal or paternal when I could based on trees or the fact that I could reliably identify the other segment with that address range. where there was no overlap I provisionally marked it as a potential recombination and/or crossover point until/unless an overlapping match turned up. Then I set about classifying segments based on the big cousins where I could. I tried Visual Phasing in the cases where segments were big enough. I used triangulation to test my assumptions.

    I used logic to interpolate as many big cousins from 23andme and ftdna who had not posted to gedmatch. I also use a system coding ancestry matches based on who they match even where the line was unknown when necessary (e.g. “mystery cluster z”). My biggest takeaways from my approach were as follows (1) how often I would have been wrong relying on Ancestry without segment matching, (2) how interconnected those of us with deep US southern early colonial era ancestry are and (3) the hell of Scottish pedigress 🙂 ….BUT my biggest challenge has been the problem of “magic thinking” regarding probability SO THANK YOU FOR YOUR PATIENCE AND WISDOM!

  43. I am researching family for my fiancé,he was adopted. On Ancestry DNA I have found people who are showing up as second cousins to him. And there are numbers beside their names such as this :465 centimorgans shared across 21 DNA segments ,407 centimorgans shared across 20 DNA segments. What does that actually mean? Because in my case I had someone show up as a second cousin and she was actually my aunt my dad’s half-sister . So how am I to tell if these people who are coming up a second cousins ,predicted second cousins for him or actually second cousins and not a first cousin or something else ?Thank you

  44. Hi, what in the world does this mean?
    This is my first and biggest hit, he’s a white dude in Virginia, I was born in Mexico.


    Shared DNA 12,9% (934‎ cM)
    Shared segments 25
    Largest segment 78,1‎ cM

  45. That is a nice close match, perhaps a first cousin or half uncle, what are your relative ages? Where did you test? Did you think you knew all your bio relatives?

    This calculator can be very useful

    Forget about that white thing, we are all human and all mixed, mexicans often more so than many!

  46. Kitty, Thanks for the great information. I have someone who matches my fiancé for one segment of around 27 centimorgans on chromosome 16 and a couple of other segments on two others. She has six segments of around 3.5-4 centimorgans on the X. Given she is a match on other chromosomes of over 7 would several smaller segments on the X indicate an X match?

  47. Hi Kitty – Thanks for this information. Question. I have at least 12 DNA matches to both me, my aunt and uncle and all of these matches are of the same surname. Because we are related to these matches 7-9 generations (according to Gedmatch) back I reduced my Gedmatch search to 3 cMs and 300 SNPs. Total segments in common vary among our 12 matches anywhere from 23 to 6. Total shared cMs range from 96.5 to 21 cMs. Would you say this was indicative of a shared ancestry?

    • I would not reduce it that far. I use 5cM and 400 SNPs when lowering thresholds for known family. But the segments are still likely to be false if the SNP count is low.
      However from what you are saying this is a set of matches worth pursuing which may well include a common ancestor. Warning, if they are from a group that has intermarried alot, then this could be misleading.

  48. I am adopted and I entered my DNA in Eventually, by matching basic DNA data from ancestry with two relatives (who turned out to be a cousin and half-sibling) I was able to determine the identity of my birth mother. I was able to conclusively do this by using other information, such as ages, time periods, and non-identifying information from the adoption agency. Now I think I have found the family, generally, of my birth father, But I don’t have any of the additional historical information to augment my search, One relative on my father’s side registers 1,767 cM across 50 DNA segments, Another registers 999 cM across 40 DNA segments. I haven’t yet been able to convince either to go through GedMatch. I’m assuming the first is a half-sibling and the second is a first cousin. Is there any way besides comparing downloaded data to make a conclusive determination? One thing that confuses me is that in the case of two half-siblings on my mother’s side we shared 60 DNA segments exactly, but in the case of the one relative on my father’s side who registered 1,767 cM we share only 50 DNA segments. Shouldn’t half-siblings, whether they come from one side or the other, share the same number of DNA segments with me?

  49. Hi. I’m following a line that comes from the Azores so endogamy is confusing me. The lines starts a while ago so any DNA match to do with that line will be 3rd or 4th cousins. Would a match that shares 50Cm on one segment be better to follow than a match that shares a total of 50Cm across 4 segments?

  50. HI,

    On my GEDMatch I have 2 matches where I am curious and have a question regarding.

    One is a match that shares 214 cM total with the longest being over 39cM… what level of relation would that hypothetically be?

    The other only shares a total of 53.7 cM however I only have one segment of 53.7 cM in length that I share with them. Is there a reason that we would share a segment so large, but it only be one segment? Would that be a relation worth looking into?

    Thanks in advance for the info,


  51. Natasha –
    There is a calculator which you can use to figure relationships out at:
    The 214 is likely about a 2nd cousin.
    The single large segment can be anything from a 4th to an 8th cousin. Segments can last for a surprisingly long time and the further away the relationship the wider the range of shared DNA. I find that single segment matches are often too far back to find so look at other matches first.

  52. Hi my brother did an ancestry DNA test and was matched 1557cm across 57 segments to someone . I don’t fully understand this and now my whole family is in turmoil as he is insistant that the person who is matched with us /him is our older half sibling. This person has found their birth mother who actually named my father’s uncle as the person’s father.

    Please could you explain what all this means and would my brother be matched this way if the person NOT my fathers child?

    Thank you

    • Sally,
      DNA does not lie. With that amount shared this match likely really is your half sibling.
      One other possibility is that this person’s mother is also a relative of yours so the match shares DNA from both sides. In that case the uncle could be the father. But DNA is more reliable than a birth mother’s statement.
      The other possibilities do not match your description of his age. Use this calculator and plug in the numbers
      Tell your brother he can send me more information via my contact form (like GEDmatch kit numbers) if he wants more proof/evidence.
      Take a deep breath and welcome your new relative into your lives.

  53. I had my DNA done. One of my dads sisters; my (aunt) came up as my cousin. How is this possible the cm 1015 the segment was 37. I asked her about she said no honey I am your aunt. The number don’t line up.

  54. Hello,
    I just had my DNA tested and I matched one person with 403 centimorgans across 23 segments of DNA, what does that translate to?

  55. I match someone at 64 cMs on one segment and we can’t find anyone in common on our trees. Do you think this could be a link to an unknown 2nd G Grandfather?

    • Fay –
      How many segments? Which company?
      This is usually in the 3rd-4th cousin range but can often be two further back ancestors or … many variations. Once you are past 2nd cousins DNA gets more and more amorphous and varied in how much you share …

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