During the last meeting of the Maine Genealogical DNA Interest Group, someone asked if it is better to have a tree that is deep or a tree that is wide. I mentioned that, for autosomal DNA test matches, a wide tree is best. The sheer number of potential 5th and 6th cousins is daunting. But, more importantly, the likelihood of your sharing DNA with a 4th cousin is only 69% and the likelihood of sharing DNA with a 5th cousin is only 30%.[i] Consequently, knowing your 10th great grandparents is of little use in matching DNA cousins. (Consequently, knowing your 10th great grandparents is of little use in matching DNA cousins. There are two exceptions to this, Y-DNA tree (paternal only) is useful for connecting trees on a Y-DNA match. Also, X-DNA can provide a similar usefulness.)
The importance of having a wide tree was exemplified recently. I was contacted through 23 and Me by a, potentially, 2nd to 4th cousin (I’ll call B.J.) I took a look at the match using 23 & Me‘s new She and my aunt Barbara shared 88cM across five segments. My mother shared 50cM across two segments; interestingly enough, I also shared 50cM across two segments. Looking at what segments all four of us share is an excellent example of how sticky DNA segments are. All three of us shared the same sticky chunk of DNA.
We exchanged basic tree information, she mentioned her ancestors were a Mannin and a Barnett. When she said that, I knew we were related and I was pretty sure I knew exactly how. Nancy Ann Mannin married Jessie Monroe Barnett about 1867 in Kentucky. They later moved to Minnesota and settled May Township in Cass County, Minnesota.
A couple more email exchanges and I learned that B.J. and my Aunt Barbara were third cousins their common ancestor was Enoch Mannin. Enoch was one of those pivotal people in my genealogical research and I knew a lot about him and his descendants. I even had B.J.’s mother (but not her father nor her) in my family tree records.
Thanks to 23 and Me for providing the tools to connect with another cousin.
I have tested my mother, my aunt, and myself with 23 and Me – Have you?
[i] Internet: DNA Land – “Face it: DNA cannot find all your relatives” https://medium.com/@dl1dl1/face-it-dna-cannot-find-all-your-relatives-f68089b8e1e9#.1yar6d4d6