Sunday, April 14, 2019

Now THAT'S a Large Segment

My parents recently took 23AndMe tests (thanks to them for humoring me yet again).  My mom's came back in record time, while my father's is still processing nearly a week after my mother's finished.  Looking at my mother's matches, there was one that looked really interesting:
My mother's shared DNA with Natalie

My mother shares a huge 72.91cM segment on her X chromosome with a woman named Natalie.  I contacted her and quickly got a response.  Natalie looped in her brother Bob who has done significant genealogical research on their family--and Bob has also tested on 23AndMe.

Bob shared a 23cM segment with my mother on the X, part of Natalie's 72cM segment.  So the implication is that the connection would be through Natalie & Bob's mother's side.

Bob was already on GedMatch and Natalie soon uploaded her data, so I was able to compare them to all of my relatives' kits.

While there are small DNA segments on the non-X chromosomes, since everyone here is Jewish, that isn't surprising with endogamy at play--and those segments may or may not have been passed down the same route as this large X segment.

Looking at my other kits compared to Natalie's & Bob's, several descendants of Chaim & Mindel (nee Eizikovics) Joshowitz also triangulate on segments of that large X segment shared by Natalie & my mother; since my mother descends from a son of Chaim & Mindel, the X segment would have had to come from Mindel.  Several of those descendants also share small segments on the other 22 chromosomes, but they are small enough that they may or may not be from other lines, thanks to endogamy.  Mindel was born in Subcarpathian Ukraine, with her family in that area back to at least the 1820s.

Bob & Natalie's maternal grandfather's family was from Siedlce Province in Poland.  Their maternal grandmother's family was from Kock, Poland, back to at least the 1820s.

So geographically, our families lived quite a distance from one another for at least 200 years.  And the fact that there are no other large segments shared between Bob/Natalie and Chaim/Mindel descendants imply that there likely isn't an NPE in the mix causing this match.  So it seems that this one large segment has been passed down intact through two lines, for over 200 years!

I wanted to look at other people who have shared DNA on the X chromosome with both my mother and Natalie, but right now GedMatch Genesis says that feature is not yet available.  But perhaps that will help us understand this better.

So meanwhile, has anyone else seen such a large X segment persisting for so long?

UPDATE:  Dmitry Pruss commented on Facebook and made me realize that this segment is NOT as old as I thought.  Bob received his mother's entire X chromosome.  Since he doesn't share this entire segment, part of Natalie's shared segment is from each parent.  So the shared segment hasn't persisted for generations--Natalie is the first to have the entire segment on her branch! AND ANOTHER UPDATE:  As Andrew Millard says below, that isn't the case.  I need to get a good night's sleep before blogging, apparently.

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  1. "Bob received his mother's entire X chromosome" is not correct. Bob received his entire X chromosome from his mother, but it could be any recombination of her two chromosomes. Natalie got a different recombination from their mother, so the different sharing does not require some of Natalie's X to come from their father.

    1. You're right. I don't know what's up with my brain today!

  2. Per FTDNA, I am a distant cousin to Scott Joshowitz and Jim Joshowitz. Any clue on which side of their family that might be?

    1. How distant? Because of endogamy, it would be a surprise for anyone with Jewish ancestry not to match at least some of the kit I administer. :)

  3. You share that trait with Israel Pickholtz.

    As to Scott and Jim, the total I share with them are 79 and and 78 cM and the longest blocks I share with them are 14 and 16 cM, respectively.
    I know: it's endogamy. But I was still curious how we are related, as I knew Jimmy from the days that I lived in Cleveland, and he visited there.