Then there's the DNA on the Y chromosome -- a small sex chromosome found only in men. Of the 23 pairs of chromosomes in the human body, the Y chromosome is the most
stable. Other chromosomes swap DNA regularly, but the Y chromosome is passed almost entirely intact from father to son like a sealed time capsule. Because of this, it's a window into male heredity -- when you look at a man's Y chromosome, you're also looking at the Y chromosome of his father, his father's father and so on through thousands of generations. You're looking into ancient history, to an ancestor who lived 100,000 years ago or more. Like SNPs, specific Y DNA sequences are associated with certain groups that evolved in isolated populations, passing certain mutations from one generation to the next until they were prevalent -- creating, for example, the so-called Native American and Viking Y chromosomes.
And finally there's mitochondrial DNA -- the female
ancestral equivalent of the Y chromosome. Every person, male or female, inherits mitochondrial DNA (mtDNA) from his or her mother through cellular organelles called mitochondria, which produce energy for cell functioning. It's a packet of DNA that, like the Y chromosome, remains essentially intact. So when scientists look at a person's mtDNA, they're looking at that person's mother's mother's mother and so on, back to the Ice Age. All mtDNA sequences found in humans fall within 36 different types called haplogroups, and Bryan Sykes, an evolutionary geneticist at Oxford University, has traced these sequences back to 36 hypothetical "mothers" who originated in different parts of the world. (He used this DNA research as the basis for his best-selling book The Seven Daughters of Eve.) So, depending on which mtDNA sequence you have, companies that run this test can tell you whether you descended from Ursula, who lived 45,000 years ago in Greece; Helena, who lived 20,000 years ago in the northeast Pyrenean foothills; or 34 others from around the world. And once Family Tree DNA has identified your mtDNA sequence, it will enter that information into a database full of sequences from more than 3,000 people to put you in touch with your Genetic Cousins -- a term they coined (and trademarked) for people with similar Y chromosome or mtDNA sequences.
By the time I developed this level of understanding about the various tests, it became clear that in two out of the three cases -- Y chromosome and mtDNA tests -- the results were far more likely to illuminate what might be called genetic anthropology (a genetic snapshot of, and connection to, people who lived thousands of years ago) than the classic genealogy of family trees and ancestors with only a handful of "great"s in front of their names. Still, according to Martin Richards, an evolutionary geneticist at the University of Huddersfield in the U.K. who did some of the mitochondrial DNA research that led to the mtDNA test, African ancestry should be among the easiest things to test for. "There are a lot of specific genetic differences between Africans and non-Africans," he told me, "which means if you have any African ancestry, it stands out." Similar differences exist in most ethnic groups. They're just more prevalent in Africans because of the isolation in which the continent's population evolved. (Like most scientists I talked to, Richards is quick to point out that these differences have nothing to do with superiority or inferiority.) I asked the folks at DNA Print Genomics whether they could look at my DNA and tell me if, say, my grandfather's great-great-grandmother was a black woman. From your DNA, it's doubtful, they said, but from your grandfather's DNA, quite possibly. When I asked the founder of Family Tree DNA the same question, he didn't hesitate: "Yes," he said, "absolutely."
So I ordered the tests: mitochondrial and Y chromosome tests for my maternal grandfather from Family Tree DNA, to learn about the ancient men and women he came from, and to take a shot at finding long-lost Genetic Cousins. The same for my father, to get a full picture of my genetic history from both sides. Then from DNA Print Genomics: nuclear DNA tests all around -- one for me, my brother, father, mother and her parents -- to see what ethnic groups we came from.
The companies express-mailed DNA collection kits around the country to my family members. The next morning, all six of us rubbed the insides of our cheeks with something that looked like the spawn of a Q-Tip and a toothbrush. (After 30 seconds of such cheek brushing, the instructions said, these devices would be swarming with hundreds of thousands of cells.) Then we carefully sealed the swabs in envelopes and tossed them in FedEx drop boxes thousands of miles apart.