Father figures

I know this because of the talks I give to the general public. Speaking to non-scientists about science is fun (as well as part of our solemn duty to obey our munificent funders) and the Jefferson story is a good one to tell, with its ingredients of sex, race, slavery and genetics. Thomas's wife Martha predeceased him by 43 years, and Thomas was true to his word never to marry again. But it was alleged that he had a relationship with one of his slaves, Sally Hemings, and may have been the father of her six children [1].Genetics entered the picture in 1998 when Eugene Foster, a retired Virginia pathologist, realised that Y-chromosome testing might be able to shed light on the controversy. He traced living male-line descendants of Sally's first and last children, Tom and Eston, and to provide a comparative sample carrying the 'Jefferson' Y chromosome recruited male-line descendants of Thomas's paternal uncle Field Jefferson, since Thomas had no acknowledged sons of his own. The notion was to compare Y chromosomes, and ask if there was a match between Sally's and Thomas's descendants.We and our colleagues analysed Y-chromosomal markers (SNPs, STRs and a minisatellite) in these samples [2], and showed that Eston's descendant, John Weekes Jefferson, did indeed carry the same Y-type as the Field Jefferson descendants. This finding supported the belief that Thomas fathered Sally's last child. The evidence is strengthened by the great rarity of the Y chromosome, now known to belong to haplogroup T1a* [3] - the sharing is unlikely to be a coincidence. Of course, a weakness of any such Y-chromosome analysis is that any other man in Thomas's patriline (his brother Randolph, for instance) would have carried the same Y, and the two possible fathers cannot be formally distinguished by DNA analysis. However, historians helped here, by providing the telling circumstantial evidence that Thomas and Sally were together at Monticello nine months before the birth of each of her children