Main Page - Latest News

DNA Research: Tibetans developed unique abilities in only 3,000 years.


From Physorg.com

The genome-wide comparison, performed by evolutionary biologists at the University of California, Berkeley, uncovered more than 30 genes with DNA mutations that have become more prevalent in Tibetans than Han Chinese, nearly half of which are related to how the body uses oxygen. One mutation in particular spread from fewer than 10 percent of the Han Chinese to nearly 90 percent of all Tibetans.

“This is the fastest genetic change ever observed in humans,” said Rasmus Nielsen, UC Berkeley professor of integrative biology, who led the statistical analysis. “For such a very strong change, a lot of people would have had to die simply due to the fact that they had the wrong version of a gene.”

The widespread mutation in Tibetans is near a gene called EPAS1, a so-called “super athlete gene” identified several years ago and named because some variants of the gene are associated with improved athletic performance, Nielsen said. The gene codes for a protein involved in sensing oxygen levels and perhaps balancing aerobic and anaerobic metabolism.

The analysis revealed that the common ancestors of Tibetans and Han Chinese split into two populations about 2,750 years ago, with the larger group moving to the Tibetan plateau. That group eventually shrank, while the low-elevation Han population expanded dramatically. Today, the Han Chinese are the dominant ethnic group in mainland China. The Tibetan branch either merged with the people’s already occupying the Tibetan plateau, or replaced them.

“We can’t distinguish intermixing and replacement,” Nielsen said. “The Han Chinese and Tibetans are as different from one another as if the Han completely replaced the Tibetans about 3,000 years ago.”

The Tibetan and Han Chinese genomes are essentially identical in terms of the frequency of polymorphisms in the roughly 20,000 genes, though some 30 genes stood out because of dramatic differences between the Tibetans and the Han.

“We made a list of the genes that changed the most,” Nielsen said, “and what was fascinating was that, bing!, at the top of that list was a gene that had changed very strongly, and it was related to the response to oxygen.”

The SNP with the most dramatic change in frequency, from 9 percent in Han Chinese to 87 percent in Tibetans, was associated with lower red blood cell count and lower hemoglobin levels in Tibetans. That variation occurred near a gene called EPAS1, which earlier studies suggest is involved in regulating hemoglobin in the blood as a response to oxygen levels. The mutation may be in a transcription factor that regulates the activity of EPAS1.