Sunday, February 2, 2014

DNA Says We Are Fourth Cousins

Bennett Greenspan, of Family Tree DNA, opened his presentation at the IAJGS Conference in Boston with something like "If we just looked at the raw data, all those of Ashkenazic Jewish descent would show up as second cousins."

This, of course, is a result of the relatively small pool of Jews in Europe a thousand years ago and the fact that for hundreds of years, most of them married within that pool. So your actual sixth and seventh cousins may look several generations closer because you have a handful of connections on your "other sides" two-three-four or more hundred years ago.

So Bennett says that FTDNA has an algorithm for its Family Finder (autosomal) test that takes this into account in order to give a more realistic estimation of cousinhood.

But even after that adjustment, I show 342 matches that FTDNA says are "suggested fourth cousins." That's not 342 fourth cousins in the world, that's 342 fourth cousins who have done Family Finder testing with FTDNA.  A result like that is patently absurd.

For comparison, they show me with forty-eight suggested third cousins.

The question is, are any of the suggested fourth cousins truly that. Let me bring two examples.

Is Moshe Hersch the son of Nachman?
I have long believed that Moshe Hersch, the top of the RITA family is the son of Nachman (b. ~1795) of the LAOR family. I believed this because these were two of the only three Skalat Pikholz families where the given names Nachman and Getzel put in an appearance. (The third is the TONKA family, which I discussed two weeks ago.)

So when we began our family DNA project, it seemed to me that this was one of the theories we would actually be able to test.
A & B are second cousins. X & Y are probably half-first-cousins-once-removed, but it's a bit more complicated..

Two people from each of the two families did Family Finder tests and because of their requests for privacy, I refer to them here as A, B, X, and Y.  A and B are female second cousins from the RITA family, but actually they are a bit closer genetically because A's grandparents are Pikholz first cousins.  

X and Y are male descendants of Josef Pikholz, of the LAOR family. X is his great-grandson. Y is either the grandson or the great-grandson of this same Josef Pikholz, but from a different (non-Jewish) woman. The diagram above shows Y as Josef's grandson.

(Y has also done a Y-37 and matches other Pikholz perfectly, so we are quite certain the family story about Josef is correct.)

If Moshe Hersch is Nachman's son, A and B are fourth cousins of X,  and third or fourth cousins of Y, so that is what I was looking for. But that was before I realized that a designation by FTDNA as a "suggested fourth cousin" is likely a generation or three more distant..

Here on the left are the results as suggested by FTDNA. B is correctly matched to A and X, but not matched with Y at all. Y is further than expected from everyone, probably because his other side is not Jewish. A and X show up as third cousins instead of fourth, but that can be explained by A's double dose of Pikholz DNA due to the first cousin grandparents.

But as I wrote above, if FTDNA gives "fourth cousin" results that are not really fourth cousins, can we really accept these results when they are convenient? That doesn't sound rigorous to me.

So I did two chromosome browsers, one based on X and one based on A. (I couldn't do browsers based on B or Y because they do not match one another.)
The matches shown here are three or more centiMorgans.

Nowhere on these two analyses do we see a place where all four match.

Both analyses show a tiny overlap of A, B and X towards the left end of chromosome 8. There are also overlaps of B, X and Y on chromosome 12 and of A, B and Y on chromosome 5.

I'm not sure that implies the kind of relationship we really want, but maybe it is.{shrug}

This is longer than I had anticipated, so the second example will wait for next week.

Housekeeping notes

1. We are now into Adar and next Sunday we remember my father's father

2. My friend and fellow Skalat researcher Jurek Hirschberg is now an authorized translator between Polish and Swedish (both ways). And he speaks a fine English.

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