Genes-R-Us — Sharing a set of ‘super’ grandparents and other blood cousins
Posted: Wednesday, October 19, 2011 5:01 pm
While I participated in Direct to Consumer (DTC) genetic testing for health-related information, my ancestry results have been thoroughly entertaining — my own mystery novel. Another unanticipated treat was finding hundreds of new cousins among all the other DNA-hungry customers. Now these are living breathing cousins — my contemporaries. We are related through a common recent ancestor, that is, a shared set of “super” grandparents somewhere in the last seven to nine generations.
No secrets are safe with DNA testing. Some people have found previously unknown siblings; while others have found out that they were not siblings at all — or at least not full siblings. Whoops. Adoptees with no connection to their biological family pay for testing with the hope of acquiring some medical history and family connection. Some of my cousins want to be in e-mail contact and are happy to share their DNA results with me. Yet other cousins refuse to believe that we are related and want absolutely no contact. Be gone, cousin.
As of the time of this writing, I have 659 new cousins based on the comparison of our SNPs. SNPs are those special DNA “letters” that vary between individuals. Most of our DNA is the same as that of other humans on the planet — but that little bit of difference has such a big effect. In past columns we have observed that SNPs have been the key to unlocking our ancestry; relatedness is no different.
Of the 3 billion DNA “letters” in our genome, less than .005 percent are SNPs. An SNP takes on only one of two values and has a chromosomal location. There can be hundreds of thousands of DNA “letters” in between two “consecutive” SNPs. Consecutive does not mean the SNPs are “next door neighbors.” Consequently having 500 or more “consecutive” SNPs is hard to come by unless two individuals have some recent common ancestor. There is a greater chance of missing a true relative than of calling some random stranger a cousin who is not.
Obviously, each person will have different results and over time will acquire more cousins as additional people are tested. I average about 10 new cousins a week. My closest new cousins to date are third cousins — so far I have 5 of them. A third cousin and I have the same great, great grandparents. I have 32 great, great grandparents; my third cousin also has 32 of them. We share 2 in common out of the 64.
As you might expect, as cousins are more distantly related, there are more of them. I have 120 DNA-identified fourth cousins, 532 DNA-identified fifth cousins and two distant cousins. Of my 659 new cousins, 76 percent were born in the U.S., 11 percent were born in Canada, while the bulk of the remainder is from Europe or Australia.
My cousins have a wide range of mtDNA and Y-DNA haplogroups, indicating a wide range of ancient ancestral migration patterns. The table below summarizes the percentage of my 659 cousins originating from a migration tied to the continent group displayed. (I used my own custom “magical” mathematical formula to do this allocation.)
Nancy’s Cousin Haplogroup Migration Spread:
MtDNA (“Eve”) Y-DNA (“Adam”)
Europe 34% 84%
Near East 31% 10%
Africa 11% 6%
Asia/India 24% 0%
More of my male cousins have gone in for this DNA testing “stuff”: 56 percent of my cousins are male, while 44 percent are female. My female cousins have no Y-DNA haplogroups and thus have no inputs for my continental spread calculation. Notice how the ancestral “Eve” has much more spread over the four continent groups than the ancestral “Adam.” This makes sense, given that the average age of “Eve” haplogroups is 40,000 years ago and the average age of the “Adam” haplogroups is 20,000 years ago.
Based on the shared DNA, 80 percent of these cousins are fifth cousins (we share same great-great-great-great-grandparents), 18 percent are fourth cousins (we share same great-great-great-grandparents), and 2 percent are third or distant cousins. One of my distant cousins is a Micmac Indian chief — and a female at that. We are related through my dad’s mother’s side of the family. I know this because I have the test results from both of my biological parents. However, this is not the Indian I am looking for, as her mtDNA and mine do not match. The chieftess and I share a common of set of French super-grandparents.
Next week: Finally we get into the health-related results.
Editor’s note: Nancy Miller Latimer has worked in scientific research and development for 27 years. She blogs at neuronalbeauty.blogspot.com. Published in The Messenger 10.19.11