Monday, February 28, 2011

A Success Story and The Randomness of Autosomal DNA Inheritance

While working with 23andMe's ancestry tools this week, I came across what I think is a really good example of the randomness of autosomal DNA inheritance.

I was contacted by one of my predicted 5th cousins who informed me that his closest match on Relative Finder is my mother's first cousin V.  According to 23andMe, they share .73% of their DNA with four matching DNA blocks, varying in size from 5 cMs to 37 cMs, 55cM total. This amount of shared DNA would imply that they are 3rd cousins, as it is just under the expected percentage of .781.

We were able to determine that he and Cousin V are 4th cousins once removed and he and I are 5th cousins. Our common ancestor couple are my (and his) fourth great grandparents Maria Latva-Jussila (1792-1865) and Yrjo Keski-Koski (1792-1861) from South Ostrobothnia, Finland.

Upon first analysis, it appears that this new cousin is more closely related to Cousin V, however that would also mean that he is more closely related to my mom and to me too. My mother and V share exactly the same Finnish ancestors and are of the same generation with no other ancestral lines in common. However, he only shares .14% with my mother (10cMs), a little bit less than what would be expected for fourth cousins, which they are (once removed). He shares about the same with my mother's sister and none with my sister who is his 5th cousin. He also shares the same (.14%, 10cMs) with me and another of our relatives who is his fifth cousin once removed. Further, my mother and I don't share any of the same blocks of DNA that he shares with Cousin V and my aunt only shares one of the same small blocks and another small unique one. To me this all clearly demonstrates just how random DNA inheritance really is.

He and Cousin V's relatively large amount of common DNA must be chalked up to a genetic fluke. They just happened to inherit more of the same DNA from the same ancestors than would be expected on average. I would like to believe that they are also related through my mom's and Cousin V's grandmother's unknown line, but if they were, then we would ALL have more DNA in common with him, not just Cousin V.

On another note, I am very happy to have found a documented cousin using Relative Finder. Those have been too few and far between in the last year. From my experience and from what I hear from others, it looks like that may be starting to change. Let's hope the recent successes finding the common ancestor from Relative Finder matches continue and multiply.


  1. Wonderful news!
    I am still trying to establish a link with any of my 990 genetic matches. I remain hopeful . . .

  2. Good luck Jody. Please let me know if there is any way that I can help.

    1. CeCe: I have been trying to find out my ancestral ties, if any, to a particular individual born in mid 1600's. I took FamilyFinder and my son took Ancestry. We both have cousins connected to this individual "distant". I, having taken FamilyFInder nad only 3 cousin matches. My son, having taken had 15 cousins matches who identify as descendants of this individual. What are the odds that thse "distant cousins" point to my being a descendant of this indivudual a well?