http://www.pbs.org/wnet/aalives/2006/science_dna2.html
Learning From DNA:
Reading Genetic History with Henry Louis Gates Jr.
The Gates family had long believed that Jane Gates -- Henry Louis Gates' great-great-grandmother -- had a relationship with a former slave owner, Samuel Brady, and a good deal of circumstantial evidence and family legend, even among Brady's white descendants, seemed to support this belief. To test the theory, Dr. Gates visited Dr. Rick Kittles, a geneticist at Ohio State University. Genealogist Jane Ailes, herself a descendant of Samuel Brady's, contacted two distant cousins who are both direct descendents of Brady, and Dr. Kittles tested their Y-chromosomal DNA alongside Dr. Gates' sample. The results lay the family legend to rest -- Dr. Kittles finds that there is no match; Dr. Gates' Y-chromosome is not the one shared by the two confirmed male Brady descendants -- and neither Henry Louis Gates nor anyone in his direct line of male descent is a descendent of Samuel Brady.
Dr. Mark Shriver
Gates had always known that his family line had included one or more white ancestors -- there were light-complected people on both sides of his family, going back several generations. To learn more about his admixture, Dr. Gates turned to Dr. Mark Shriver, at Penn State University, and contributed a DNA sample. What he learned surprised him, even given his awareness of his white heritage.
According to Gates' admixture test results, his genetic heritage was 50% European and 50% African -- half of his ancestors, according to Dr. Shriver, were white. That meant that perhaps four of his eight great-grandparents were white, or all eight had a white parent of European descent.
But who were these white ancestors? Working with Dr. Kittles, Dr. Peter Forster, and Dr. Fatimah Jackson, Dr. Gates did further lineage testing, and found even more surprising results. His mtDNA tests revealed the most matches in northern Europe and only a single match on the African continent, in northern Africa, near Egypt -- very unusual for an African American; who would expect to find European matches in his Y-chromosome lineage, among his male ancestors. But Dr. Thornton and Dr. Heywood, working with documentation of Dr. Gates' family, parts of which had lived as free people since the time of the American Revolution, developed a well-supported hypothesis: that Dr. Gates is probably descended, on his mother's side, from two indentured servants, living during the colonial period, a black man and a white woman......
....Dr. Shriver first identified groups of genetic markers commonly found in the European genetic components of African Americans' admixture, and excluded these markers from the chip, and therefore from the analysis. This made it possible to zero in exclusively on Dr. Gates' West African genetic origins.
The test results were then compared against a database of individuals from several West African ethnic groups. The results of the analysis show where the subject's markers are clustered relative to know African ethnic group. In this way,
he found a close match for Dr. Gates among the Mende people -- introducing him to his distant relatives and revealing, at last, his roots in Africa.
