Dr. Erlich said the technique works best for people who have the highest participation in genetic genealogy services, upper- and middle-class Caucasian Americans.

WSJ: Researchers Identify Anonymous DNA Donors

Some genealogy sites group such genetic information with surnames.

WSJ: Researchers Identify Anonymous DNA Donors

It includes DeCode Genetics (nasdaq: DCGN - news - people), the company that made news with its plan to use the genealogy of the people of Iceland as a tool for genetic research, and Exelixis (nasdaq: EXEL - news - people), which uses model systems like fruit flies to figure out what genes do in human beings.

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