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A basic test primer

So the fall DNA sales are over.

The Thanksgiving holiday sales have just wrapped up.

And — any day now — we can expect the winter holiday sales to launch if they haven’t already.1

And, before they do, The Legal Genealogist owes some readers an apology.

Because folks like me who’ve been doing DNA testing for a decade or two tend to forget that not everybody has been doing DNA testing for a decade or two.

So… before the next sale… a DNA test primer, to help those who’ve entered the field more recently — or are just getting ready to stick their toes in the DNA waters — better consider what test they might be interested in, and why.

DNA results

There are three basic types of DNA tests: autosomal, YDNA and mitochondrial DNA (mtDNA) tests. Each one can be extremely valuable for genealogical research, but in very different ways. Autosomal testing — the basic cousin finder test — is available from all the major testing companies — 23andMe, Ancestry DNA, Family Tree DNA, MyHeritage DNA and Living DNA. It’s the least expensive, entry-level test. The other two DNA tests for genealogy — YDNA and mtDNA testing — are done only by Family Tree DNA among the major testing companies. These are more expensive tests but can be more powerful in answering specific genealogical questions.

Let’s look at each in turn.

Autosomal testing is, as noted, the basic entry-level test offered by all of the major DNA testing companies It is, in fact, the only test done by all of the companies except Family Tree DNA, where it’s called the Family Finder test.

This sort of test looks at the kind of DNA we all have and all inherit from both parents. Anyone can take this test, male or female, and it will compare the test taker’s results against the results of others in the database of the company where the test was done to match up with relatives — cousins near and far. It will identify any relationship up to second cousin (shared great grandparents) for sure, and a wide variety of more distant cousins as well. But because of a random mixing of genes through the generations (a process called recombination), not all more distant cousins will share enough autosomal DNA to be detected as matches.2

This is the test that will estimate your ancestry by percentage from different parts of the world.3 Of course, the emphasis when it comes to those percentages is on the word estimate. The numbers are really good at the continental level (Europe, Africa, Asia) and marginal (and occasionally flat out wrong) when it comes to any smaller geographical region. Take the percentages with a grain of salt — or the whole darned salt lick.4

Because of the relatively low price of this test — even when it’s not on sale, it’s the most reasonably priced DNA test of all — and because the best function of this test is to help us find cousins with whom to collaborate and share research, this is usually the test we should all start with. It’s fun, it produces the most bang-for-the-buck for beginners, and it’s an easy way to “fish” in the databases for relatives we can connect with.

YDNA testing looks at the kind of DNA that only men have and that’s passed down from father to son to son in a direct male line, largely unchanged from generation to generation.5 So this test can only be done by men (ladies, we need to get a brother or male relative to test for us) and it looks only at the DNA of our direct paternal line — our father’s father’s father’s line. Among the major testing companies, only Family Tree DNA offers YDNA testing.

Even the entry level YDNA test — 37 markers — is more expensive than an autosomal DNA test,6 So what’s the benefit of doing YDNA testing? It can definitively identify two male testers as related — or not related — in one specific line, that direct paternal line. And, because YDNA does doesn’t change that much from generation to generation, it can do that going many generations farther back than autosomal testing can.

So if your research question is “could my John Smith be descended from that John Smith who lived in Culpeper County, Virginia, in 1700,” you’re very unlikely to get a DNA answer you can rely on by using autosomal DNA — the common ancestor is so far back in time that two test takers today may well not share any autosomal DNA in common even if they really are cousins. But YDNA testing of your test candidate against a documented male descendant of that John Smith? It will be able to answer that “could we be descended” question.

Now… there are limits. If they do match, the test can’t tell the two men exactly how they’re related, or who the common ancestor is. It can tell them they are both descended from one man, somewhere back in time, but — by itself, without paper trail evidence — can’t put a name on that man. And if they don’t match, it won’t tell them why they don’t match.7 But it’s a great place to start looking at that direct paternal line.

Mitochondrial DNA (mtDNA) testing looks at the kind of DNA we all have but that is passed down only by a female to her children, and then only by the daughters to the grandchildren, and so on. So an mtDNA test can be done by anyone — male or female — but it only looks at the DNA of our direct maternal line — our mother’s mother’s mother’s line.8 Among the major testing companies, only Family Tree DNA offers mtDNA testing.

Like YDNA testing, mtDNA testing is more expensive than the entry-level autosomal test. Even on sale, the full sequence mtDNA test — and that’s the one we want if we’re going to do this test — is $139. So this is not a test to go fishing for relatives. But it is a test that often is the only way to answer a genealogical question.

In my own family history, I have a major issue with identifying one particular fourth great grandmother. That’s because the fourth great grandfather was catting around as a married man, and his daughter — my third great grandmother — could be the daughter of the first wife or of the woman he ran off with and later married after the first wife’s death. YDNA can’t help here since daughters don’t inherit YDNA at all. Autosomal testing is unlikely to help because the common ancestor is many generations back. But by testing my mtDNA against the female line descendants of both women (or their sisters or their mothers), I should be able to rule in one candidate and rule out the other.9

So these are all good tests for genealogical research, but one may be better than another for a specific research question. Think about what you want to know when you sit down to review the sale prices.

Cite/link to this post: Judy G. Russell, “Before the next sale,” The Legal Genealogist ( : posted 6 Dec 2020).


h/t to one of my proofreaders Barbara Zimmer for catching the typo…

  1. Some have — check out the holiday sale at Family Tree DNA for example. Or the holiday sale at 23andMe. Or…
  2. See ISOGG Wiki (, “Autosomal DNA,” rev. 21 Oct 2020. As for recombination, see ibid., “Recombination,” rev. 14 Apr 2019.
  3. Ibid.
  4. See Judy G. Russell, “In 2020, still not soup…,” The Legal Genealogist, posted 13 Sep 2020 ( : accessed 6 Dec 2020).
  5. ISOGG Wiki (, “Y chromosome DNA tests,” rev. 30 Oct 2020.
  6. In the current Family Tree DNA sale, this entry-level YDNA test is $99 on sale, compared to the autosomal Family Finder test, sale priced at $59.
  7. See Judy G. Russell, “Back to basics: YDNA,” The Legal Genealogist, posted 31 July 2016 ( : accessed 6 Dec 2020).
  8. ISOGG Wiki (, “Mitochondrial DNA tests,” rev. 10 Aug 2020.
  9. See generally Judy G. Russell, “Why chase that mtDNA?,” The Legal Genealogist, posted 23 June 2019 ( : accessed 6 Dec 2020). And yes, for those who are wondering, I’m a lot closer to an answer… just not quite close enough to start writing it up…
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