Monday, August 11, 2008

Genealogy Gets More Precise

Rapidly growing databases enable a more complete picture of one's ancestry.

By Emily Singer

Credit: Technology Review

Tracing your ancestry via DNA is becoming a popular pastime, thanks to a growing number of consumer tests available over the Internet. At least two-dozen companies sell tests ranging in price from $100 to $900, and public interest is thriving. Most of these tests, however, paint a very rough picture of an individual's ancestral origins: they're limited to the direct maternal or paternal line. But that is beginning to change.

New technologies are allowing scientists to search for markers across the genome that can more precisely predict ancestry. Much of that data is being poured into public databases, supplying much more accurate and detailed information to genetic-testing companies and new consumer tests.

The basics of genetic ancestry testing are this: scientists search for genetic markers that appear more frequently in one population than in another. By combining the information gleaned from a number of markers--anywhere from tens to thousands--researchers can estimate the percentage of an individual's ancestry from different parent populations.

Most genetic ancestry testing to date has focused on genetic markers in the mitochondria, which everyone inherits from their mothers, and on the Y chromosome, which males inherit from their fathers. Commercial tests using these markers have sparked harsh criticism from the genomics community, which contends that the public doesn't adequately understand the limited view of an individual's origins that the tests provide.

Now, both the scope and resolution of genomic ancestry studies are growing dramatically, thanks to specially designed microchips that allow scientists to quickly scan hundreds of thousands of spots on an individual's genome. That means that researchers can gather genetic information from more people in more places, generating better ancestry markers. In addition, the ability to find markers across the entire genome, rather than just within mitochondrial or Y-chromosome DNA, generates a more complete picture of one's ancestry.

One recent effort has focused on distinguishing subsets of the European population, a challenge because, as a historically young population group, Europe has a comparatively low level of genetic variability. (Africa, on the other hand, has more genetic diversity than the rest of the world combined.) "We can easily determine the difference between northern and southern [European] populations and a number of different groups within either," says Michael Seldin, a geneticist at the University of California, Davis. "However, in some cases, it's difficult. There are lots of Italian individuals we can't separate from Greeks, and Northern Italians we can't separate from the Spanish."