'Blond Genes' May Vary Around the World
Scientists say DNA for fair hair in South Pacific differs from that in Europe
Thursday, May 3, 2012
The genetic variant that causes many dark-skinned people from the Solomon Islands to have blond hair is different from the gene possessed by blond Europeans, the study found. Researchers from Stanford University School of Medicine found that this particular variant is absent in the genomes of Europeans.
"Since most studies in human genetics only include participants of European descent, we may be getting a very biased view of which genes and mutations influence the traits we investigate," study co-senior author Carlos Bustamante, professor of genetics at Stanford, said in a university news release. "Here, we sought to test whether one of the most striking human traits, blond hair, had the same -- or different -- genetic underpinning in different human populations."
The frequency of blond hair in the Solomon Islands is between 5 percent and 10 percent, the researchers said.
"They have this very dark skin and bright blond hair," study co-senior author Sean Myles, a former Stanford postdoctoral scholar who is now an assistant professor at the Nova Scotia Agricultural College, said in the release. "It was mind-blowing. As a geneticist on the beach watching the kids playing, you count up the frequency of kids with blond hair, and say, 'Wow, it's 5 to 10 percent.'"
Many locals assumed their blond hair was the result of sun exposure or high fish consumption. Others believed it was a trait passed on by European explorers. The study authors, however, sought to determine if there was a unique genetic basis for this characteristic.
In conducting the study, which is scheduled to be published in the May 4 issue of Science, the researchers assessed Islanders' hair and skin color using a light reflectance meter. The investigators also took participants' blood pressure, measured their heights and weights, and collected 1,000 saliva samples from the villagers to examine their DNA.
To look for the genes associated with blond hair, the researchers then selected 43 of the most blond and 42 of the darkest-haired Islanders from the samples collected, and looked for differences in the frequency of genetic variants between the two groups.
The researchers immediately identified a single signal on chromosome 9, which accounted for 50 percent of the variance in the participants' blond hair. They later identified the gene responsible, called TYRP1. The authors noted that the genetic variant that leads to blond hair among people in the Solomon Islands is not found in the genomes of Europeans.
"Within a week we had our initial result," the study's co-first author, Eimear Kenny, said in the news release. "It was such a striking signal pointing to a single gene -- a result you could hang your hat on. That rarely happens in science. It was one of the best experiences of my career."
"The human characteristic of blond hair arose independently in equatorial Oceania," she said. "That's quite unexpected and fascinating."
"This is one of the most beautiful examples to date of the mapping of a simple genetic trait in humans," David Reich, a professor of genetics at Harvard University who was not involved in the study, said in the news release.
The study authors said the finding underscores the need for genetic studies on isolated populations.
"If we're going to be designing the next generation of medical treatments using genetic information and we don't have a really broad spectrum of populations included, you could disproportionately benefit some populations and harm others," Bustamante said.
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