Why Your DNA Test Results Are Wrong

7464252264_a12645770a_kOkay, scratch that. They’re not ALL wrong. They’re just…wrongish.

DNA test sites meant for genealogical use typically give you an estimated degree of relationship, so you have some sense of where to start when figuring out how you’re related. GEDmatch, a popular DNA analysis tool used by many genealogists, also gives you an estimate, by telling you how many generations it thinks there might be between your new cousin and the common ancestors you share.

The more I nail down my cousin matches, the more I realize how many grains of salt you should take those estimates with. At this point, I might need a little red wagon to haul around my giant salt shaker.

Let’s take my cousin Amy’s test. Amy was one of my first matches, and we’re listed at FamilyTreeDNA as second-to-fourth cousins.

When we uploaded to GEDmatch, we compared DNA, and we were listed at 4.6 generations to the most recent common ancestor (MRCA). Your parents are the first generation, your grandparents are the second generation, and so forth. Essentially, GEDmatch things we’d be roughly third or fourth cousins. That’s a bit more distant than FamilyTreeDNA says, but it’s in the same ballpark (and I think FamilyTreeDNA’s estimates are on the optimistic side, although that’s strictly from my own observations and experience).

In three years of searching, Amy and I haven’t been able to find the match. Amy is an adoptee, so that complicated things considerably, but even now that we’ve finally discovered her biological father’s family, we still haven’t figured out the connection to me.

Then we tested Amy’s great aunt, on the side where we know we relate. This great aunt is two generations closer to the MRCA, so she should shed more light on our connection, right? Nope. Her great aunt matches me on the same chromosome Amy does, with almost exactly the same segment length, at a distance of 4.6 generations to the MRCA.

How can Amy and her grandma’s sister be the same number of generations away from the common ancestor? Because DNA doesn’t behave exactly the same in each generation, or each couple, or each baby. It’s rogue. If it were a person, it would have those big earhole things and 16 eyebrow piercings and a penchant for flipping off any genealogist who tries to tell it how to behave. DNA is basically an obnoxious teenager.

Next, let’s look at my cousin Norskie. He’s on GEDmatch, along with his son and grandson. Guess what? All three of them share virtually the same segment with me. Three generations of cousins, all showing at 4.9 generations to the MRCA. That’s DNA flipping you off right there.

Keep this in mind when you’re trying to make sense of your DNA matches. The estimates you see as to how related you are are not etched in stone. They’re etched in sand, at best. Keep an open mind when you’re considering how you might be related to a new match.

Note: If you want to learn more about how to use GEDmatch, join me this weekend at the Family Tree University Virtual Conference. I’ll be presenting on GEDmatch basics, and showing how I used the Tier 1 tools available to donors to discover the match with the three generations of Norskies mentioned above. There are two other DNA presentations as well, plus a live chat. I’ll also have a presentation on using tagging in Evernote to analyze (not just organize) your genealogical research. See you there!

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