Wednesday, March 22, 2023 -
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DNA testing — who goes first?

Part 1 on my DNA series looked at why to test for genealogy and ethnic estimates. Part 2 explored who the big testing companies are, the best place to start, and how to actually take the test.

Who to test?

Now, let’s look at who in your family should get tested first.

Because of the nature of DNA inheritance, and the law of diminishing returns, we need test older folks ASAP. If you are lucky enough to have your parents still alive (or better yet, your grandparents) — test them first. If both your parents test, there’s no need for you or your siblings to, since your parents gave you (and your siblings) all of your DNA, and your parents have more of it. Aunts and uncles are good sources also, if you parents aren’t available or willing.

But for many of us, our parents are gone, so we need to test ourselves — and if you have older cousins, that’s helpful. Also, test your siblings if possible — although they inherited roughly 50% of your parents DNA, they got different mixes of DNA than you did (unless they’re identical.) That means they will have DNA matches that you won’t, which can be very useful.

By the way, men or women can take the autosomal test (at-DNA) at Ancestry, 23andMe, MyHeritage or FamilyTree DNA.

Your matches

Reviewing, there are two reasons to take a DNA test: ethnicity estimates, and matches.

I’ve talked about ethnicity estimates in the last two columns, so let’s talk about those matches. Depending on the company, you can get anywhere between 1,500 and 200,000 people on your match list that share DNA with you.

Due to endogamy (generations of intermarriage), Jews will almost always have a lot more matches than non-endogamous populations, which can be great and simultaneously overwhelming. But the match list is the key to finding relatives and therefore, breaking through some brick walls that records and documents can’t. I’ll emphasize here that it is vital that you work on finding records before or while you’re working on your DNA matches.

DNA by itself proves very little, but when combined with research, it can be amazing. I’ll soon talk about how to use that match list.

The two other DNA tests

In Part 2, I mentioned that most people take an autosomal DNA test, although the testing companies don’t generally call it that. But there are two other kinds of DNA test.

One of those tests is for the male line only (patrilineal), tracing back your surname (last name) at birth. It’s called the Y-DNA test, and only men can take it, since women don’t have Y chromosomes (they have two X chromosomes.) However, women can get a male relative (brother, father, uncle, paternal cousin) to take a Y-DNA in their stead, and it’s just as accurate in tracing that name. That test can trace that line back hundreds of generations back, far beyond when reliable records were kept, since the sex chromosomes change very little over time.

The third test is a mitochondrial test (mt-DNA), and traces back only the matrilineal line (mother’s mother’s mother). Even though only women can pass down mitochondrial DNA, both men and women can take that test, and it also goes back hundreds of generations.

The Y-DNA and mt-DNA tests are only available from one company, FamilyTree DNA, which also offers at-DNA tests. They’re a bit more expensive than autosomal tests, although they go on sale regularly, as do all DNA tests, especially around holidays.

Doing a Y-DNA or mt-DNA test can help narrow down matches on either the patrilineal or matrilineal lines. If you have a common last name, an at-DNA test might give you hundreds of matches with that name, but the Y-DNA test can narrow those names down significantly. The same could be said of the mt-DNA test, but matrilineal lines are more challenging, since most American women changed their surnames every generation, if they married.

Most people start with the most common test (autosomal) and depending on the mystery they’re trying to solve, might take one (or both) of the other two tests later. I suggest starting with taking the Ancestry test first, and working with the matches — which I’ll talk about next time.

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