Thursday, July 9, 2015

Cousins of Cousins

A DNA cousin at 23andMe shares identical DNA with my father and three of his close cousins- each from a different branch of the tree.  This is why you need to see the segment(s) shared between DNA cousins and you need to test your own close cousins to narrow down which branch of your tree may hold the common ancestor.

The match to my father will be in his Duryea and Cummings branch because the segment of DNA is shared with the cousin from descended from Abraham Brewer Duryea (1878-1944) and Nellie Cummings (1879-1965).

The segment shared between the DNA cousin and the cousin from the Uhl and Patschke branch could match anywhere in the cousin's entire family tree.

Same for my cousin from the Cook and Neal branch- the common ancestors could be anywhere in his tree (but not too far- they may be about fourth cousins).  Matching my father does not narrow down the possibilities because my father's shared segment with this DNA cousin can be attributed to another branch.

I cringe when people write to me about DNA cousins in common when they don't match on the same segment.


  1. I just send them to the triangulation article on my blog

  2. Thank you, Kitty. A great idea! I will refer people to articles specific to their query. I will write some more posts based on the most common questions or issues I see in my inbox.
    I'm lucky in that I have many close cousins DNA tested. I've been comparing DNA cousins to my entire family for years, so I am used to a DNA cousin matching several of my family members who are from different branches.
    The next article illustrates how misleading cousins in common can be, utilizing my mother and my maternal Irish third cousin:

  3. You are welcome Jody, I also have lots of cousins tested which is very very useful!