I've written many times about how I always share way more DNA with known relatives than would be expected for given relationships, which isn't a surprise since endogamy is at play. So when I asked my newly-discovered cousin Anne (who found me via my blog) to take a DNA test, I expected that we should share quite a bit of DNA. After all, my grandfather was her half second cousin.
Well, Anne's results came in. We do not appear on one another's match lists on FamilyTreeDNA. I did a one-to-one comparison on GedMatch, which did show a small shared segment:
If I hadn't tested family members, I'd be questioning the paper trail and whether Anne and I were truly related. But Anne has very good matches with other members of my family, including my mother.
Although Anne shares 3 nice-sized segments with my mother, I simply didn't inherit any of them.
In addition, Anne has incredibly good matches to other members of the family who have tested. The following graphic shows tested individuals in yellow. The first number is the total number of shared centimorgans Anne has with each person (according to GedMatch), and the second is the largest segment size.
Anne shares large amounts of DNA--and some very large segments--with the majority of relatives who have tested. The exceptions to those sharing large segments are myself and my third cousin Mark (with whom the largest shared segment is only 9.8cM).
When you have Jewish DNA, it's always suggested that you concentrate on matches with large segments in common. But regardless of ethnicity, it's important not to disregard the potential relationship of matches with smaller (or no) amounts of DNA in common as being unrelated if the paper trail suggests otherwise. While I knew theoretically that it was possible for half second cousins twice removed to share no DNA, I didn't expect it to happen in my entirely endogamous family.
Both Mark & I are half second cousins once removed to Anne. And we share so little DNA that we don't appear as potential matches to Anne. But the amounts of DNA that Anne shares with other family members makes it clear that the paper-trail relationship is correct.
Oh--and that 8.3cM match that I have with Anne--it comes from my father. In fact, look at my father's shared DNA with Anne:
My father actually shares more than three times the amount of DNA with Anne as I do--even though there's no paper trail connecting them. Thanks, endogamy!
Note: I'm on Twitter. Follow me (@larasgenealogy).
Well, Anne's results came in. We do not appear on one another's match lists on FamilyTreeDNA. I did a one-to-one comparison on GedMatch, which did show a small shared segment:
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| My DNA Comparison with Anne |
If I hadn't tested family members, I'd be questioning the paper trail and whether Anne and I were truly related. But Anne has very good matches with other members of my family, including my mother.
 |
| My mother's shared DNA with Anne |
In addition, Anne has incredibly good matches to other members of the family who have tested. The following graphic shows tested individuals in yellow. The first number is the total number of shared centimorgans Anne has with each person (according to GedMatch), and the second is the largest segment size.
 |
| DNA Anne Shares With Cousins |
When you have Jewish DNA, it's always suggested that you concentrate on matches with large segments in common. But regardless of ethnicity, it's important not to disregard the potential relationship of matches with smaller (or no) amounts of DNA in common as being unrelated if the paper trail suggests otherwise. While I knew theoretically that it was possible for half second cousins twice removed to share no DNA, I didn't expect it to happen in my entirely endogamous family.
Both Mark & I are half second cousins once removed to Anne. And we share so little DNA that we don't appear as potential matches to Anne. But the amounts of DNA that Anne shares with other family members makes it clear that the paper-trail relationship is correct.
Oh--and that 8.3cM match that I have with Anne--it comes from my father. In fact, look at my father's shared DNA with Anne:
 |
| My father's shared DNA with Anne |
Note: I'm on Twitter. Follow me (@larasgenealogy).
I recently tested a presumed relative who would be about a 5th cousin to me. FTDNA showed no match between us; however, she matches my full sister as a 4th to remote cousin, with 103 cM (longest segment, 10 cM). She also matches a lot of my close and distant cousins. So, after many years of corresponding with her, I can finally say that she is truly my cousin, even though we don't match on DNA.
ReplyDeleteNot enough to prove or disprove with dna at that distance and with those sorts of results.
DeleteDistant cousin is all she is saying, Lara. That seems reasonable.
DeleteA very important reminder for genetic genealogy. Thank you!
ReplyDeleteGood point. And, of course, the reverse is also true. You can share DNA with someone and NOT be related. That happens to me much more often than the opposite.
ReplyDeleteWell, when you're endogamous, those people aren't closely related, but they're still related at some level--just maybe further back than the algorithms state.
DeleteRight. I don't have a thousand 2d-3d cousins. At best these people are seventh or eighth cousins, and we will never know how since very few of us can trace our ancestors back before they were using surnames.
DeleteTesting your sister and brothers might produce different results than your own.
ReplyDeleteVery true.
DeleteIt took me several years to find a known living Halperin relative, and I sent her a DNA test only to find we didn't "match" via Ancestry DNA. I am encouraged by your research that this wasn't some sort of mistake made by Ancestry!
ReplyDeleteYup. A non-match (for a distant enough relative) doesn't mean a non-relative.
Delete