Strategy for targeted testing

Time and again, The Legal Genealogist hears the lament: “I don’t have any male in my line to do a YDNA test!” Or, “I don’t have the right person in that line to do an mtDNA test!”

In some cases — many fewer than you might think — those statements may actually be true.

We know, of course, that YDNA is the kind of DNA that only males have and that is passed down from father to son to grandson and so on, largely unchanged through the generations.1 And it’s possible that there really may not be a single living male in the direct paternal line you need (or you might not be able to find one) to do that YDNA test.

And we know that mitochondrial DNA — mtDNA — is the kind of DNA that we all have but that is inherited solely from our mothers, who got theirs from their mothers (our grandmothers) who got theirs from their mothers (our great grandmothers) and so on.2 And it’s possible there too that the person whose mtDNA haplogroup we’d dearly love to identify may not have left a single descendant in that direct maternal line.

But in the vast majority of cases it’s a matter of choosing a different candidate for our testing.

Of looking up, over, and down for the right person to test.

Even when it means looking up and up and up, then over, and then down and down and down for that right person.

Let’s say you really really want to know if your paternal line descends from Niall of the Nine Hostages3; you want that cool badge on your DNA results that says he’s in your paternal line.4 But you’re the one and only child of your father, and you’re female. And he was the one and only child of your grandfather. And he was the one and only child of your great grandfather. So you have no brothers, no cousins, no uncles to test.

You need to look up, over, and down.

Keep going up the generations of your family tree in that line until you find one that didn’t result in a lonely only. Somewhere back in time, and — given human reproductive patterns — likely not that many generations in the past — you’re likely to find a male who had male siblings. Stop there and go over to the siblings — every one of the males you can find. And then come back down their family trees looking for that one living son of a son of a son who’s willing to take a DNA test for you.

Up over and down

So in this illustration, you — as the female with no brothers, no living father, no uncles, no male cousins — you’d go up your line past your lonely-only grandfather and past your lonely-only great grandfather back to your second great grandfather… who had a brother.

Go over to that man, who’d share that YDNA you’re looking for: both he and your second great grandfather would have inherited their YDNA from your common ancestor, your third great grandfather.

Then come down his line to every living male among his descendants. Those folks in the last generation are fourth cousins — and have the same YDNA your father had.

The same thing works for mtDNA except that you’d be looking for the female-line descendants of daughters of a common female ancestor, rather than the male-line descendants of a common male ancestor.

The beauty of both YDNA and mtDNA is that they tend to be so stable — changing so little from generation to generation — that we can keep going up the generations as far as we can trace the records to find that one male or one female who had descendants that will produce the test candidate we need. If we can find that test candidate we can be matched with him or her even if many generations stand between us and our most recent common ancestor.

That’s much less likely to be true with the more common autosomal DNA tests, where our chances of matching drop off quickly: even at the third cousin level, one out of every 10 pairs of third cousins won’t have enough DNA in common to match; at the fourth cousin level, about half won’t have enough in common to match; and at the fifth cousin level, nine out of 10 may not have enough in common to match.5

But for both YDNA and that direct paternal line and mtDNA and that direct maternal line, the odds are that you’ll run out of records to find the test candidate long before you run out of DNA to match.

So don’t give up too fast on the idea of getting an answer to a research question with YDNA or mtDNA.

And don’t ever give up until you look up, over, and down.


SOURCES

  1. ISOGG Wiki (http://www.isogg.org/wiki), “Y chromosome DNA tests,” rev. 4 Dec 2016.
  2. Ibid., “Mitochondrial DNA tests,” rev. 1 Aug 2017.
  3. Wikipedia (http://www.wikipedia.com), “Niall of the Nine Hostages,” rev. 26 Dec 2017.
  4. See “What does the Niall of the Nine Hostages badge on my personal page mean?,” The Family Tree DNA Learning Center (https://www.familytreedna.com/learn/ : accessed 6 Jan 2018).
  5. Ibid., “See What is the probability that my relative and I share enough DNA for Family Finder to detect?.”
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