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Roots: Using DNA to Trace Genealogical Roots

Publication Date: 
June 29, 2008
Source: 
60 Minutes
Author: 
Lesley Stahl

Henry T. "Hank" Greely was interviewed for this segment of 60 Minutes:

Genealogy, researching family history, is one of the most popular hobbies in the country, right up there with gardening. A nation of immigrants, we almost all come from somewhere else we wish we knew more about. So searching for our roots holds tremendous appeal. And today, there's an exciting new addition to the genealogist's tool kit: genetic genealogy. It turns out that inside each one of us, within every single cell of our bodies, is information about who our ancestors were, where they lived and who we're related to today. Our DNA contains hidden stories about our past, and as we first reported last fall, scientists, together with businessmen, are now offering ways to help us read them.

...

STAHL: And that's the rub. This business of genetic genealogy is fraught with limitations. For one thing, it can only provide information about a tiny fraction of our ancestry. Because we get half our DNA from our mothers and half from our fathers, almost all of our DNA gets shuffled and remixed every generation, making it impossible to trace what comes from whom. There are just two bits of DNA that remain pure. The Y chromosome, which passes directly from father to son, and something called mitochondrial DNA, which passes unchanged from mother to child. Hank Greely, a law professor at Stanford University, has studied this new field. He worries that people don't realize just how many ancestors they actually have.

HANK GREELY: Eight generations ago, both you and I had 256 great, great, great, great, great, great-grandparents.

STAHL: Wait, you're saying that if you go back eight generations...

GREELY: Uh-huh.

STAHL: ...we have 256 great, great, great, great-grandparents?

GREELY: Yes. It doubles every generation. So, you've got two parents, you have four grandparents. You have eight great-grandparents. Sixteen great, great-grandparents. And it adds up fast. It adds up so fast, in fact, that if you go back 20 generations, you've got over a million grandparents.

STAHL: One million, forty-eight thousand, five hundred seventy-six, to be exact. And in each generation, DNA testing can provide information about only two of them.

Mr. GREELY: So you could be Peruvian on your mother's, mother's, mother's side, Japanese on your father's, father's, father's side. Swedish on everything else.

STAHL: And you'll never know?

GREELY: And you'll never know the Swedish from the Y chromosome or the mitochondrial DNA.