Saturday, February 03, 2018

A closer look at shared segments

What's happening on Chr 18?
In my previous blog post, A DNA match who shares 3 different kinship paths, I had observed that while my Mom had two segments on Chr 18 my Brother appeared to have one long segment shared with the match. Looking at the Chromosome browser graphics(using the legend) you can see that there is a little "skip" in the segment.   A no call in my Mom's results, maybe?  

Which shared segments are shared by all 3 siblings?
I wanted to get a clearer picture of how the shared segments survived or didn't from one generation to the next.  I'm adjusting the segment number that my Mom shares with this match to 12 segments as the two Chr18 segments are really likely one long segment.  There are only 3 segments of the 12 that all three of her children also share. That's 25% of the shared segments that were passed to the next generation.  Or 75% which didn't get passed down--at least in this case.  Notice too that my brother only received a portion or the Chr 6 segment. So only 2 segments passed to all 3 of us in their entirety.  My two brothers who have not tested may have gotten different segments or they may have the same three that my brother, sister, and I share.  Neither of the brothers who haven't tested have any children.

 It would be interesting to see if these three segments made it thru to my nephew and nieces if they test.  My daughter didn't get any of the 3 segments which are shared by all 3 of us.  This is a great example of why you should test as many siblings as possible if you have only one parent available for testing. I really don't want to think about how many segments were "lost" from my paternal lines because my Dad never tested.  Thankfully his sister tested.   Sounds like an idea for a future blog post(s) as I have 2 sets of 2C1R to use for comparison with my aunt and my siblings on my paternal lines.

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