I read somewhere that 50% of people do a DNA test for the ethnicity estimate. Which probably explains why 50% of the questions in the Facebook genetic genealogy groups I’m a part of start with “I did a DNA test and why does it say I’m X when I’m not X?” Or conversely, “why doesn’t it show any X ethnicity when I was told I had X ethnicity?” (with X almost always being Native American).

The questions that are not about ethnicity are usually along the lines of “is this normal?” Most people don’t know that up to 10% of third cousins and 90% of fifth cousins don’t share any DNA. This post is going to explore why we don’t see ethnicities we think we should see, and why we don’t share DNA with all our more distant cousins. I’ll talk more about how ethnicity estimates work in another post.

Did you know you actually have two family trees? Genealogists use the term “paper tree” to refer to ancestors you can trace back using traditional genealogical methods, such as birth, death, marriage and census records. The term “genetic tree” refers to ancestors you inherited DNA from. Obviously, there’s a lot of overlap there, but your genetic tree is only a small subset of your paper tree. Given that we can only have as much DNA as we can have, there’s just not enough room to have a piece of every single ancestor’s DNA. Further, even if you inherited a piece of DNA from a particular ancestor, it is possible that the segment is too small to be useful. If you read my post “DNA in a Nutshell,” you will understand that once a segment gets too small, it’s entirely possible that it matches another person who has that segment totally by chance, and not because you share a common ancestor. I imagine that when comparisons are made for ethnicity estimates, the same idea holds true. Tiny amounts of DNA that match a particular company’s reference population for a particular ethnicity are likely not counted.

Obviously, if your genetic tree contradicts your paper tree, there’s an issue that needs to be resolved. For example, if you don’t share DNA with a close cousin, or you don’t share DNA in the expected range, someone’s paper tree is going to have to be updated. But absence of evidence is not evidence. Not sharing DNA with a more distant cousin or not having a particular ethnicity show up in your estimate does not mean that your paper tree is incorrect. If it’s DNA proof you’re looking for, finding a relative who matches you as they should and also matches a particular cousin and/or has the particular ethnicity show up will do -a great-aunt or uncle works well here if there isn’t a grandparent, an aunt or uncle if there isn’t a parent. People who are only half-related to you (like a cousin) are not really good candidates, because they might have inherited those segments from an ancestor you don’t share, but it’s better than nothing if there’s no one else to test. If the DNA is on a straight maternal or paternal line, mt DNA or Y DNA testing will assign you a haplogroup. You can use this information to see if your haplogroup is consistent with haplogroup of a particular ethnicity.

To sum up, your genetic tree is only a small part of your paper tree, so while it’s disappointing to not match with certain cousins or to not have a particular ethnicity show up in your estimate, it doesn’t mean there’s something incorrect in your paper tree. Maybe Native American DNA is just not that into you.