Monday, January 2, 2012

My Close Relatives on 23andMe: Paternal Second Cousin Once Removed

I recently got results for my dad’s second cousin.

Here is how Ron matches with his second cousins -- nothing unusual here. Second cousins are expected to share about 3.125% of their DNA, and everyone shares approximately this amount with Ron.

Things start to get weird when looking at the comparisons between Ron and my three sisters and I. We are second cousins 1x removed, and would be expected to share about 1.5% of our DNA.

One of my sisters has a fairly normal match to Ron, although her percentage is slightly above average. Surprisingly, she passed on every single segment perfectly intact to one of her daughters. Her other daughter got most of the segments -- she shares about 70% of the DNA Ron shares with her mother compared to the expected 50%.

My dad's other three children have only a very small match to Ron. We share about three or four times less DNA than expected. These results are more consistent with a fourth cousin as opposed to a second cousin 1x removed.

After looking at this comparison, it might be tempting to conclude that because we have such a small match compared to the average percentage for second cousins 1x removed, our dad probably had a smaller than average match too.

However, there is no evidence to suggest this.

If you add up all the unique segments that my dad’s four daughters inherited from him, it’s 13 + 43 + 38 + 29.5 + 18.5 + 44 = 186 cM = at least 2.48% of DNA shared between my dad and Ron (there’s also a decent chance that Ron and my dad shared segments that none of his daughters happened to inherit). This percentage is slightly below average for second cousins (2.48% compared to 3.125%), but not dramatically low.

However I only received 26 out of 186 cMs, or about 14% of Ron’s shared DNA compared to the expected 50%. My sister inherited a piddly 13cM out of 186cM, or about 7% of the shared DNA. Sister #3 inherited 30 cM out of 186 (16% of the shared DNA). Sister #4 seems to be skewed in the other direction -- she inherited 157cM out of 186cM (84% of the shared DNA).

Can I coin a ‘new’ saying?

“Recombination is like a box of chocolates, you never know what ya gonna get!”


Jason Woodward and Dorotha Drew Woodward, our common ancestors.
Thanks for the DNA!

No comments:

Post a Comment