Friday, August 17, 2012

Sorting The Parental Matches and WOW!!!

23andMe has been adding some new features, some of which are helpful to us genealogists, such as family tree capabilities.  A new feature was added today which will greatly help some of us:  sorting your matches into paternal and maternal.

Let me clarify first:  You have two sides to every chromosome.  Twenty two of your twenty three chromosomes have two sides consisting of the side from your mother and the side from your father.  Current science, or the science available to us genealogists, cannot tell you WHICH side- maternal or paternal- is reflected in any one of your results.  As such, autosomal DNA tests produce a pool of genetic matches from both of your parents and you need to sort through them by comparing family tree and triangulating DNA matches with other known close relatives.

The new paternal and maternal sorting feature at 23andMe only works if you have a parent in the database who is sharing genomes with you.  In my situation, I have both parents in the system, so this works very well for me.  This feature does not work at all for my parents because their parents are dead and not in the system.

I set up my family tree and linked my parents to me and voila!  Of my 1600+ matches, 600 are credited to my mother and 200 to my father.  There is no specification for the other 800.  Very correctly, the people who match both my mother and father are credited as such.

I eagerly looked to see if my mystery 5% match from one year ago was attributed to my mother or father, especially since this person is blocked in my parent's account because the relation is too close.  As I hoped (feared?), this anonymous close relative is my mother's cousin.

My mystery second cousin is as close as my mother's first cousin or uncle.
Who is he?

See the pink M by the predicted relation of 2nd cousin?  That means that this person related to me on my mother's side.  So who is he?

We can use the mitochondrial DNA (mtDNA) to rule out some possibilities.  MtDNA is passed from mother to child; males do not pass mtDNA to their children.  My mtDNA group is H1, the same as my mother and her uterine brother, and the same as their mother, Jeannette ODonnell.  Jeannette's four siblings are also all H1, so this man is not a sibling of my grandmother because his mtDNA group is H3a.  It is possible that this person is a son of Jeannette's brothers, or an unknown half-sibling of Jeannette by her father.

Basically, the percentage of shared DNA drops in half for every generation removed or is cut in half when the relation is by one ancestor instead of two.  Full first cousins (two grandparents in common) match 12.5%, while half first cousins (one grandparent in common) match 6.25%.  This is to put in perspective how close a relation this 5% match is to me.  Double that for one generation up and you have an approximate 10% relation to my mother.


  1. Thanks, CeCe!
    I am trying to compute who this could be. Looks like I only have to go back to grandparents, maybe great grandparents, then back down. Absent an adoption, I should know this person.

    1. Yes, you don't have to go back very far! Have you figured it out? Do you have any repeated great grandparents on your mother's side of your tree that would increase the DNA shared? If not, this is very likely your first cousin once removed.

    2. In my downloaded Ancestry Finder Matches, I can see the 15 segments that I share with this cousin. When I compare them to where I match my mother's half brother, 10 of these 15 segments line up. He must be a cousin or nephew of my maternal grandmother.