The Promise of DNA

As the paper documents for researching my family are starting to peter out, I’ve become interested in taking a look at DNA as a means of filling in some of the blanks and to reinforce some that might be a little too circumstantial. So I sent my sample off to Family Tree DNA. I chose them because in addition an autosomal DNA similar to those offered by AncestryDNA and 23 and me, they will test your Y-DNA and mtDNA.

DNA testing is for your genetic relationships. In other words, you have a genealogical tree that contains all your cousins, ancestors, etc. based on your paper research. And you have a genetic tree that contains only those ancestors that contributed to you DNA. While there is overlap, not everyone in your genealogical tree contributed to your DNA since bits and pieces are lost each generation. After about 5 generations, your genealogy tree will be much larger than you genetic tree.

In short, the atDNA is that which you get from both parents. Roughly, you get 50% each from your mother and father. And it roughly halves with each generation back. So you get 12.5% from each of you four grandparents and 6.25% from each of your eight g-grandparents. This test is good for finding genetic (vs genealogical) cousins. It’s likely you’ll share DNA with your genealogical cousins up to about the 4th cousin relationship, but the likelihood declines rapidly after that. So this test is great to find cousins who have a fairly close genetic distance. In addition, atDNA will give you a fairly accurate prediction (more on that in a future post) of your ethnic makeup.

Y-DNA is the unique DNA passed from father to son. An exact copy is passed down over the generations, but deviations do occur at a fairly characterized rate. So this test can help find paternal cousins and because the deviations are consistent, it will give a reasonable estimate of how far back our most common ancestor is.

MtDNA, on the other hand is uniquely passed down through the maternal line in that only a mother can pass it down. While I may inherit, my mother’s mtDNA, I did not pass it down to my daughters. My sister, though, will have passed our mother’s mtDNA on to her daughters. mtDNA is not useful to “fish” for cousins because it mutates very slowly. So a genetic match may be a close cousin or several generations away. I don’t have a lot of info on my maternal line, so I’m hoping this test may help me narrow my search.

More to come on my DNA experience in future posts, but I am convinced that DNA testing is as important a tool in genealogical research for proving relationships as any paper document. So much so that I have been recruiting family members to test as well. So if we’re related and you’re willing to participate, please get in touch.