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Genes-R-Us — DNA-based ancestry and the ‘recent’ family tree

Genes-R-Us — DNA-based ancestry and the ‘recent’ family tree

Posted: Wednesday, October 12, 2011 5:02 pm

Direct-to-Consumer (DTC) genetic testing companies provide two kinds of ancestry information: “ancient” and “recent.” Last week we dug into haplogroups that are used to trace “ancient” maternal (mtDNA) and paternal (Y-DNA) lines of ancestry. This week we will define what is meant by “recent” ancestry and how it is determined. By combining these two kinds of ancestry information, I uncovered some surprising family connections.
The familiar family tree helps to differentiate between “ancient” and “recent” DNA-based ancestry. All of us have:
• two parents,
• four grandparents,
• eight great-grandparents,
• 16 great-great-grandparents,
• 32 great-great-great-grandparents,
• 64 great-great-great-great-grandparents.
Of your 64 great-great-great-great-grandparents, half are from mom’s line and half are from dad’s line.
Put yourself at the root of the tree. Dad and mom are one generation from you and your grandparents are two generations from you. Placing successive V’s from you to mom and dad and from mom to her parents and from dad to his parents, there are six people in your tree, not counting you.
Now trace out the path from you to your mom and then to her mom. This is the line that your mtDNA haplogroup terminates with after hundreds of thousands of generations passing down through only the moms to you. Similarly for Y-DNA haplogroup, but we follow the daddy only line. For the tiny two generational family tree, two of your grandparents were not on either the mtDNA or Y-DNA terminal braches: your dad’s mom and your mom’s dad.
As you add more generations into your family tree, the bulk of your ancestors are not going to be on the mommy only or daddy only lines. Although their lineage may not factor into the “ancient” haplogroups, those great-great-…-great-grandparents certainly figure into your ancestry and, in particular, your race.
Your race is a “recent” event compared to your mtDNA and Y-DNA haplogroups. Your DNA-based racial calculation incorporates the races of all your ancestors from the last seven to nine generations. Those folks, from the last seven to nine generations preceding you, are what we mean by “recent” ancestry.
How frequently your ancestors reproduced will determine the exact number of generations on each branch (or line) of your family tree. If we assume that every generation is 25 years, then eight to nine generations beyond you includes 510-1,022 people and stops roughly around 1600 A.D. To put this date into perspective, the Pilgrims landed at Plymouth Rock in 1620 A.D.
Did you notice that we have not defined a DNA-based reference for “race”? Everything we have discussed up to this point assumes some kind of reference. To create such a reference, scientists must “travel” back in time before 1500 A.D. when people rarely traveled more than a few hundred miles from where they were born.
A reference definition of race uses long “runs” of SNPs (special DNA “letters”) that distinguish between people groups with different home continents. We identify these groups of people as African, Asian and Caucasian. As more human genomes are sequenced, the better that reference becomes. It is doubly impressive that the racial mix of your last seven to nine generations can be calculated separately for mom’s side and dad’s side.
For example, my father has several long “runs” of SNPs on four different chromosomes that indicate an Asian-based ancestry from his mother’s side. Although his racial mix is only 2 percent Asian, from the mathematical characteristics of his Asian-based SNPs, he is estimated to have at least one Asian ancestor between his great-great-grandparents and his great-great-great-great-grandparents on his mother’s side — a two generational fudge factor. Another bit of math matches those Asian SNPs to the more specific Native American sub-group.
I want to find this Native American ancestor in my dad’s “recent” ancestry. My father and his brother know nothing about their mom’s ancestry except that her family spoke French as their household language and came from New Orleans. My father’s “ancient” mtDNA haplogroup, X2b, is notably odd — ubiquitous but rare — with greatest frequency among the Micmac Indians of Nova Scotia and the Druze of Israel.
I consider my evidence:
a) French grandma + New Orleans =
Possible Arcadian heritage
b) Arcadian heritage =
Nova Scotia/NE Canada connection
c) Nova Scotia + mtDNA of X2b =
Possible Micmac female ancestor
Granted my Native American ancestor need not be a woman nor be in this mommy only line. Given the number of generations that I must go out on the tree, there are many other ways for this Native American to show up. Nevertheless, it seems a reasonable place to start. My plan of action is to begin with the mom’s mom’s mom’s … mom branch of my dad’s family tree.
I plow through the genealogical records in ancestry.com since our family tree does not exist. And what do I find? My father’s pure mommy line tracks back to a Frenchwoman, Barbe Bajolet Dite Bayol, 1609-1683, one of a small number of female founders of the Arcadian population. Because of her historical significance, many of her direct descendants have had their mtDNA haplogroups determined and published — and, yes, they are all X2b!
Okay, so this DNA stuff really works — but this is not a Native American. Barbe is pure European.
Bummer, now I am really going to have to work to find that Native American ancestor. Onto the next line which proves Arcadian, too. Interestingly, this line connects to a “Françoise, Count of Châteauroux, Baron de La Tour Landry” (1540-1598) in France. All the ancestors after this dude have numbers in their names. Moreover, the records just keep going back in time … when will they stop? Finally I get it — these are nobles. My Landry Arcadian line leads directly to back Charlemagne (e.742-814 A.D.), the greatest of medieval kings, and his (ahem) concubine Regina, making me his 34th generation granddaughter. (See my blog for complete line.)
Apparently it is not that improbable for those with Western European ancestry to find that they are related to Charlemagne, but the history lover in me, this is quite an intellectual treat!
…still no success in finding that Native American ancestor, but failure has never tasted so sweet!
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 10.12.11

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