Genes R US — A little spit from mom and dad goes a long way
Posted: Wednesday, September 12, 2012 5:00 pm
Initially I paid little attention to the newest data analysis feature in 23andme.com, my favorite direct-to-consumer genetic testing company. In order to use the new Family Tree feature, a 23andme.com customer must have the DNA of at least one biological parent available within 23andme.com in addition to their own.
Since both my biological parents were so kind as to spit in a tube for me, I can use this awesome tool. After I identified my parents, as such, within the Family Tree by their 23andme.com customer names, I was treated to new information for all my many DNA-identified cousins. Each cousin is now identified as being related to me through my father’s side, my mother’s side or both.
Cousins are identified by overlapping segments of DNA. The more DNA segments that overlap and the longer they are, the more closely the cousins are related.
To date I have 990 cousins in the Relative Finder, ranging from projected second cousins through distant cousins. A second cousin and I would share one set of our eight sets of great-grandparents. A fifth cousin and I would share one set of 64 sets of grandparents. A distant cousin and I would share grandparents further out than a fifth cousin.
With the new Family Tree feature, I can bypass the whole sharing invitation experience which is mostly disappointing. (I am not sure why so many people are so hesitant to share their information at the basic level.) The actual length of the shared DNA segments is only available to me if my cousin agrees to share their DNA with me at the basic level. But even without a share, 23andme.com still uses this information in establishing the likely relationship between cousins.
My very closest DNA-identified cousins are all through my father’s side. My top 25 matches (read that as 100 percent) are through my Dad’s side only. These closest cousins are projected to be second cousins up to fifth cousins. We share from 0.66 percent to 0.40 percent of our measured DNA and have anywhere from 6 and 4 overlapping DNA segments of significant length.
Of my next 100 closest DNA-identified cousin matches, 91 percent come from my father; and 11 percent come from my mother. There are two cousins that I am related to through both parents so they are double counted. For these 100 cousins, we share 0.38 percent to 0.20 percent of our DNA with relationships varying from 3rd to 6th cousins, and sharing between 3 and 2 segments of overlapping DNA.
Do you find these statistics odd? Of my first 125 cousins, a whopping 92 percent are from my father’s side only! As the cousins get more distant, they increasing come from my mother’s side. My last 125 matches are 70 percent from my mother and 30 percent from my father.
My most distant 125 DNA-identified cousins vary in projected relationship from 4th to distant cousins, sharing anywhere from 0.10 percent to 0.70 percent with only one common segment. What is going on here?
Why is it that my closest relatives on 23andme.com are predominantly through my non-Irish side? Are the Irish really not that curious about their DNA?
This all seemed so counter intuitive given that one in nine people in the US are estimated to have some Irish heritage-far more than have French heritage. I continued to puzzle over this for several hours and then it hit me. My father’s family is from a founder population.
The founder effect, which is very strong in my father’s Acadian forbearers, is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. The Acadians were drawn from the larger population in France that settled in maritime Canada in the 1600s.
After a couple hundred of years of selecting marriage partners only from this small group of Acadians, my French cousins are related to me through many multiple lines. The net effect is that I will share more overlapping of DNA segments than what would be expected for a given cousin relationship.
I realize that pondering my genetic belly button may not be as interesting to you as it is to me. I continue to be “blow away” by what I have learned through the study of my own DNA and that of my parents.
Discovering a heritage that connects me to a rich genetic and historic past has been an incredible gift to one who was adopted at birth, with no hope of a heritage. Amazingly God has used every drop of my search and research to draw me close to Him!
Nancy@NancyMiller Latimer.com has worked in scientific research and development for 27 years. She blogs at NeuronalBeauty.BlogSpot.com
Published in The Messenger 9.12.12