Reposted from:
http://www.newscientist.com/article/dn11178?DCMP=NLC-nletter&nsref=dn11178



A distinctive, repeating sequence of DNA found in people living at the eastern edge of Russia is also widespread among Native Americans, according to a new study.

The finding lends support to the idea that Native Americans descended from a common founding population that lived near the Bering land bridge for some time.

Kari Schroeder at the University of California in Davis, US, and colleagues sampled the genes from various populations around the globe, including two at the eastern edge of Siberia, 53 elsewhere in Asia and 18 Native American populations. The study examined samples from roughly 1500 people in total, including 445 Native Americans.

The team looked for a series of nine repeating chunks of DNA, known as 9RA, which falls in a non-coding region of chromosome 9.

They found the 9RA sequence in at least one member of all the Native American populations tested, such as the Cherokee and Apache people. The two populations in eastern Siberia, where the Bering land bridge once connected Asia to North America, also tested positive for the 9RA sequence.

The 9RA sequence did not appear in any of the other Asian populations examined in the study, including those from other parts of Siberia, from Mongolia or Japan.

Multiple migrations?

According to Schroeder, the high prevalence of this gene marker among native populations of North and South America - and its absence in most of Asia - lends strong support to the idea that Native Americans can trace their ancestry to a common founding population.

The 9RA mutation probably occurred in an ancestral population located at the eastern edge of Siberia, which subsequently migrated over the Bering land bridge, Schroeder says (watch how the land bridge was gradually submerged as see levels rose). There may have been multiple migrations from this founding population, occurring thousands of years apart, she adds.

"How many times did people cross the Bering land bridge? That would be a very difficult question to answer," says Jeffrey Long at the University of Michigan Medical School in Ann Arbor, Michigan, US, who contributed to the new study.

Other experts have previously suggested that Native Americans do not share a common ancestry because of the linguistic and dental differences among populations.

Journal reference: Biology Letters (DOI: 10.1098/rsbl.2006.0609)