Monday, October 3, 2011

DNA Projects: It's NOT Just About Individual Results

I'm finally comprehending something that my writing partner, CeCe Moore, has understood for a long time. CeCe blogs as Your Genetic Genealogist. She has tested several family members. By comparing who (and how much) each known family member matches those whose relationship are unknown she can learn much more than she can when she just compares her own results with the match for whom she is trying to discover the actual relationship.

I have long understood this with Y-chromosome studies. I have been able to recreate the 111 markers that my 6th great-grandfather, Philip Dowell would have if we could find exactly where he is buried in that church yard is Southern Maryland, dig him up and test his DNA. Philip died in 1733. More details on the current status of the Dowell/Dewell Surname DNA Project is scheduled to be published in one of the next two issues of

My learning opportunity has come as I examine the autosomal DNA test results for my wife Denise and her sister Michele. As most of your know Y-chromosome and mitochondrial DNA often is passed down unchanged for many, many generations. Not so with autosomal DNA. It changes significantly with each inter-generational transfer. Most individuals share about 50% of their autosomal  DNA with their siblings. Denise and Michele share about 45%. Therefore the matches that they get on their autosomal tests at 23andMe are different. 

As of this morning, Denise had 707 matches and Michele had 797. They each have many matches not shared by the other. If you are familiar with 23andMe, you will understand that we will never learn the identity of a majority of these matches. Many of those tested there did it for the medical information and have no interest in genealogy or have privacy concerns that keep them from communicating with others with whom they have a match. 

So far we have only been able to find that Michele matches two of the ten individuals with whom Denise has the longest matching segments. 

From Denise’s list:
Potential Cousin #1
3 segments, 
0.77% shared
1 segment, 
0.22% shared
Potential Cousin #4
1 segment, 
0.34% shared
1 segment, 
0.19% shared

As we continue to contact those with whom the sisters share identifiable segments of autosomal DNA, we will probably fill in other shared connections. However, this preliminary comparison has been an eye opener for me. I knew autosomal DNA was fickle, but I am only beginning to understand how randomly it is distributed from one generation to the next. It takes the results from multiple family members who are known to be related to begin to piece together a coherent picture.

No comments:

Post a Comment