The first American to be able to claim descent from Genghis Khan has been discovered. He is Thomas R. Robinson, an associate professor of accounting at the University of Miami in Coral Gables, Fla.

Dr. Robinson's descent from Genghis Khan emerged in a roundabout way. The Y chromosome of that Mongol emperor was identified in 2003 by geneticists at the University of Oxford in England. Surveying the chromosomes of Asian men, they noticed a distinctive genetic signature in populations from Mongolia to Central Asia. Their common feature was that all but one lay within the borders of the former Mongol empire.

The geneticists concluded that the far-flung Y chromosome must have belonged to Genghis Khan and had become so widespread because of the vigor with which he and his sons labored in their harems, a fact noted by contemporary historians.

While the geneticists were collecting blood samples from the Oxus to Xanadu, Dr. Robinson was researching his family tree and had established that his great-great-grandfather, John Robinson, had emigrated from Cumbria in England to Illinois. Reaching a dead end, in 2003 he submitted a scraping of cells from the inside of his cheek to Oxford Ancestors. The company traces people's ancestry to specific regions of the world based on their Y chromosomes, which track paternal descent, or on their mitochondrial DNA, which is inherited through the female line.