Those hoping to trace their ancestry to a particular African tribe are unlikely to find a perfect match, according to a new genetic study. Researchers report that mitochondrial DNA isolated from African-Americans matched up to distinct African ethnic groups in fewer than 10 percent of cases, based on a partial database of African DNA samples. Broader or more probabilistic ancestries are still possible, however.

An individual's genes are a link to the past that stretches across any break in family name or birthplace through the generations. But not all genes are equally useful in tracing ancestries. The genes present on chromosomes are mixed extensively in every generation, making them a crude guide. In contrast, mitochondrial DNA is passed down from mother to child relatively unchanged, offering an individual the chance of identifying a distinct modern population, such as an ethnic group, having the same ancestors. Such reconstructions may still be imprecise, however, because mitochondrial sequences originating in one ethnic group can easily leak to others as women migrate.

Nevertheless, Bert Ely of the University of South Carolina wanted to see if he could use mitochondrial DNA sequences to trace the African roots of black Americans, as some companies have begun offering. ...