A few months ago I asked my 90-year-old grandmother to rub the inside of her cheek with a soft cotton swab, and then I sent it to the Genographic Project's DNA laboratory to be tested (cost is about $99). Grandma grew up speaking German, surrounded by relatives who had come from Prussia, so imagine our surprise when the results showed that she is of Haplogroup X, a DNA sequence associated with the indigenous people of North America. Grandma is an American Indian!
She scoffs at the very thought of it. There were native Americans nearby where she grew up in Northern Wisconsin, but they certainly weren't part of the family. She's German, like everyone else she new growing up. Grandma doesn't think much of those stupid DNA tests.
Well to be precise, this test looks at mitochondrial DNA (mtDNA), which is not the same thing as the DNA you inherit equally from both parents. If you remember your high school biology, every cell in your body contains a nucleus, made of "regular" DNA. But a cell also contains other material, including little energy-supplying mitochondria, which also contain bits of DNA called mtDNA.
Remember how cells divide by splitting into identical halves, each of which in turn will divide, on and on forever? Each cell in your body is the result of a long series of divisions that began when you were a single, unfertilized egg cell in your mother. That cell was also the result of a series of divisions all the way back to her mother, and so on into the distant past. That's what makes mtDNA interesting: it's from the non-nucleus (i.e. unfertilized) part of that single, constantly-dividing cell that goes way, way back into time, and since it's unfertilized, it contains no DNA from any father, ever.
So my grandmother's haplotype X comes from her mother, and her mother's mother, all the way back -- no fathers involved. And since it's just for mothers, we asked Grandma to think carefully about her mother's history, and the history of her grandmother. That's when Grandma remembered that her own grandmother, orphaned at a young age when her parents died of tuberculosis, was adopted by German immigrants! Grandma's father's side was German, but now we know what happened on the mother's side!
Since Grandma had no daughters of her own, there would have been no way to discover this fact about my family if we hadn't swapped her cheek in time. Good reason for those of you who have living grandmothers to rush out this instant and get her tested before it's too late. You may find a similar surprise in your family tree!