The question I often see is are we really 2nd or 3rd or 4th cousins? The answer is usually “maybe.” A 2nd-4th cousin designation by your testing company is purposefully vague. Best to look at the amount of shared cMs in segments greater than 7cM, number of segments, and the sizes of those segments; plus, of course, who else this new DNA relative matches!
DNA inheritance gets more and more random the further away the relationship is. The amount of DNA you share with someone more distant than a 3rd cousin is impossible to predict and even those 2nd and 3rd cousins seem highly variable. So the statistical study conducted by genetic genealogist Blaine Bettinger is deeply appreciated by all of us hunting down the relationships with our DNA connections.
Shared DNA statistics from Blaine Bettinger, used by permission
Blaine has created this beautiful chart. His blog has several posts explaining the study which is the source of these new statistics. See http://www.thegeneticgenealogist.com/2015/05/29/the-shared-cm-project/ for all his posts on this study. I had previously discussed his project when recruiting people to add their statistics; apparently he is still taking in statistics so click here to add yours.
Hi Kitty,
Thank you for publishing the table. Having a range of values is very useful; I didn’t think there would be so much variation. My DNA result came in a few days ago and so far not many of my family have been tested apparently! My best match is one 2nd to 4th cousin. He has 4 family members who I don’t match but I thought I’d try to figure out who they are to each other before I get in contact. The match himself might be from my unknown paternal grandfather’s side so I don’t have any tree to offer them.
On a different note, my mum was Dutch and your second cousin RL is a match to me with a gedmatch estimate of 5 to the common ancestor. The range of values in the table above has given me some hope, thank you!
Ingrid
I am confused by something. The chart shows a great aunt or uncle variation of 236-1301 cm. It shows an aunt or uncle variation of 121-2227 cm. Why would the closer relationship have more variation? I just got results on Ancestry DNA showing that I share 895 cm across 51 segments with my maternal uncle, so I am curious about this! it has him as 1st-2nd cousin.
Thank you,
Cori
These statistics were collected from people volunteering their numbers so there can be wide variation. Probably with more people reporting the closer relationship was wider. Hard to say. Ask Blaine.
I recently had my maternal uncle tested and the results show that he and I share 730 cm. When I add his raw data to Gedmatch, the numbers jump to 850 cm. Folks in one DNA genealogy group on FB tell me that he is definitely my half uncle. Is it possible that he is my full uncle with numbers like that, or could he in fact be my half uncle?
That is low for a full uncle but not impossible. You would need more family tests to determine if he is your mother’s half brother.
Can you test your mother or any of her other siblings? Can you test a few 2nd cousins related to just your maternal grandfather? If they do not match your uncle then he would have had a different father from your mother.
Thank you for your reply. My mother is deceased but my aunt, her sister has agreed to test as well as her son and daughter. My mother’s brother and I both tested at Ancestry DNA and he and I are sharing several “family circles” through my mother’s paternal line. I’ve recently connected with a 4th cousin through my maternal grandfather’s line and the “cousin” matches both my uncle and myself. Once I have the results back for my aunt and her two children, would it be possible to prove definitively that he is my full uncle?
Your aunt’s test will show definitively whether he is your full uncle or not. If you can upload both tests to GEDmatch you will see areas where they are fully matching (both chromosomes) if they are full siblings. Do the one to one compare with the graphic and you will see many green bars above the blue bars.
Hmm, I better do a blog post on this
I recently uploaded my AncestryDNA raw data to GEDmatch and two Munsons that show you as contact email come up as a 20.6/15.2cM match (small world). I am adopted and having a rather challenging experience tracking down my Paternal line through only DNA matches (I do know my maternal line through paper + one confirmed 3C DNA match). I am still definitely a GEDmatch noob and will be reading a lot of the reference material this weekend (including that from this site). Thanks for this blog.
Kevin –
Have a look at the materials at DNAadoption.com for advice on your search, if you have not already.
Have you tested your Y at family tree DNA? Sometimes that can give you a surname.
– Kitty
My mother and her brother were adopted. Her brother passed away in 2003, before DNA was readliy available. She found out in 2012 that they share the same mother. Father, in both cases, unknown. She just got her nephew tested on Ancestry. This is where we are confused.
We bought him into gedmatch, and on a 7cM or larger baseline they share 1167 cM, with the longest segment 165cM. I do not know how to read how many total segments they share, but if I had to guess I would think 26 (??)
On my mothers paternal family tree (I made it down to her great great grandparents through DNA) my nephew, when uploaded, also got the same connections to her same paternal line, but through different people…. Is it possible their fathers are one in the same? or is it more likely their fathers are cousins? Thank you – jen
Jen –
That is high for a half nephew but low for a full nephew. More cousin tests are the easiest way to resolve this but unti the father or father(s) are found that could be difficult.
I am working on a blog post about this issue but probably will not finish it until after the jamboree. Use my contact form to send me the gedmatch numbers and I will try to have a quick look – if there are lots of close matches on the one to many for each that are not shared it would point toward a half relationship.
The DNA adoption web site has a great chart
http://www.dnaadoption.com/uploads/DNAadoption/DNAadoption_files/DNAadoption/Combined_Relationship_Prediction.pdf
That site also has a relationship calculator discussed here:
https://dna-explained.com/2016/02/22/demystifying-ancestrys-relationship-predictions-inspires-new-relationship-estimator-tool/
I have downloaded Blaine’s very very helpful chart awhile back….but my computer has crashed, several times and I can’t find where it is in my scheme of things.
I’d like to download the chart itself again…..can you direct me to where I would find it as a stand alone document?
Thanks
Lois
Click on the image above to get it as a single document (JPEG) in your browser, but I recommend that you subscribe to his newsletter as I hear a new chart will be out soon. His blog is http://thegeneticgenealogist.com/
I was adopted & trying to prove who my birth father is. I believe I know, so I did a DNA on his grandson. I am trying to see if his grandson comes up as my half nephew, which would prove the grandfather is my birthfather. The only catch is his grandmother is my great, great aunt thru my maternal side, so we share some DNA thru her. His cM is 1122.8, the largest cM comes up 100.9. It shows us to be 1.8 generations. Does this mean he is a half nephew with a little more shared DNA thru his grandma?
Thank you for helping me in advance.
Hi MSKitty,
I sent an email on June 15th, & haven’t seen a response. I just wondered if you could help me with it.
Thank you! Annette Shields
Annette –
You left a comment and I must have missed it. But actually I prefer to answer more general questions that help everyone.
Your conclusions look valid. Congratulations. If you want more confirmation, test more people.
Thank you!
Hi, I had my nephew tested on Ancestry. Put him up with me on gedmatch. We share 727cm. To me, that says My sister and do not share the same Father. I have tested two gedmatch people with the same surname as me and both are a match. They also match my son. Surely something is wrong. Ray
Ray –
There is wide variability in the ranges. Don’t jump to conclusions although it is likely.
To confirm that your sister is your half sister get a paternal side cousin or two tested and see if they match your nephew or not.
Hi Kitty thanks for your reply to my confusion over a DNA relative match of 18.4% shares DNA . How can I prove further that this could be a half sibling as all the charts I read say a half sibling needs to have at least 19.4% shared DNA. Would this change in any way if I asked my sibling (same parents) to do a DNA test? Am very confused and not sure how to get further clarity on this. Thanks. Becky
Becky,
Have you both uploaded to GEDmatch? If not, do so. Compare the X as well there.
If you can’t test your parents then test family closely related to each of them, an aunt or uncle or first or second cousin on each side. A half sibling will only be related to one parent or the other
Hello Mr. Kitty. I’ve been searching for my biological mother and father. I did my Ancestry DNA testing and a woman has come up as a match. 1860c in 41segments. Is that pretty safe to assume she is a half sister? Thank you.
Wow… SORRY!! Meant Ms. Kitty not MR.!!!!
She could be your aunt/niece, grandparent, or half-sister.
See http://blog.kittycooper.com/2016/08/how-to-tell-the-relationship-from-the-shared-dna/
Thanks for the reply. She is 5 years younger than I am. Considering my bmom was 16 and bdad was 18…. I think she could be my half sister.
Is there a chart like this that also shows potential 1/2 relationships? So many of us are dealing with this in searching with unknown biological parents. Thanks.
He will be releasing a new chart very soon with more of those relationships. You can get a rough idea by halving the relationship in question. Also the DNAadoption site has a chart
http://www.dnaadoption.com/uploads/DNAadoption/DNAadoption_files/DNAadoption/Combined_Relationship_Prediction_Chart.pdf
Hey Kitty,
I appreciate all your efforts to help those of us who are new to DNA. Sometimes if feels like reading a foreign language. So here’s my question:
I have a (2nd) cousin who recently did her DNA on Ancestry. She wrote me to say that she got a match from another cousin (1st Once Removed) of mine. However, the 2nd cousin who did the test is on my Paternal Grandmother’s side and my 1st once removed cousin is on my Paternal Grandfather’s side. There are no family stories of marriages between these two families. Their shared DNA is 17.188 cMs across 2 segments. Is the only explanation that there was, in fact, a marriage/child involved?
Jerry –
17.8 across 2 segments can be pretty far back and is not necessaily significant. If you are from a population group that is at all intermarried (endogamous) like Arcadians, Mennonites, Jews, Polynesians then it is even less significant.
So yes those two families married somewhere way back in time, but it is too small a match to be easily found in your genealogy.
Keep reading and enjoy the process!
Hi!
If someone share 913cM across 41 segments – ancestry says 1st Cousin or 1/2 Niece/Nephew. Couldn’t this be a full Niece as well?
Sorry Debbie but no… Always plug the number into this calculator to see the possibilities: https://dnapainter.com/tools/sharedcmv4