Thursday, November 8, 2012

Double Cousin

An interesting match has surfaced among my father's genetic cousins at 23andMe.  This cousin, N. H., shares three small segments with my father.  N. H. is related on both my father's paternal and maternal sides. How do I know this?

DNA comparison between N. H. and D.W.
and N. H. and David Lutter

D. W. is my father's paternal cousin, once removed.  His DNA is so useful for sorting matches because anyone who matches both of them is related through the branch of my family tree that D. W. and my father have in common.

Here, we see that N. H. matches both my father and his cousin on the same segment of chromosome 4.  Thus, N. H. is related to my father via the paternal line.

Next, N. H. and my father share a small segment on the X chromosome.  The 23rd pair of chromosomes determines sex.  Men have XY.  The Y is passed from father to son relatively unchanged.  The X is passed from mother to son.  Thus, N. H. and my father are related through their mothers as well.  X chromosome inheritance follows a very specific path, eliminating several lines of ancestry from holding the match.

N. H. and my father also share a small segment on chromosome 8.  At this point, we cannot be sure which parent this segment can be attributed to.