In one of the "African American Lives" programs, descendants of the person Henry Louis Gates' oral history identified as his ancestor did not match Gates' Y-dna. So though he has a European y-dna, it doesn't match the family that his family had always identified as progenitor. As Gates said "It's a white man, but some other white man." I may not have quoted him exactly, but that's the gist of it.

toot