Friday, August 20, 2010

Blue eyes recent genetic mutation

One Common Ancestor Behind Blue Eyes
LiveScience: People with blue eyes have a single, common ancestor, according to new research. A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes. 'Originally, we all had brown eyes,' said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.

The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin... Rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue. If the OCA2 gene had been completely shut down... hair, eyes and skin would be melanin-less, a condition known as albinism...

Eiberg and his team examined DNA from mitochondria, the cells energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages... Over the course of several generation, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shared long haplotypes, that means the sequence arose relatively recently in our human ancestors...

'All blue-eyed individuals are linked to the same ancestor,' Eiberg said. 'They have all inherited the same switch at exactly the same spot in their DNA.' Eiberg and his colleagues detailed their study in the Jan 3 online edition of the journal Human Genetics.

Blue eye colour most likely originated from the near east area or northwest part of the Black Sea region, where the great agriculture migration to the northern part of Europe took place in the Neolithic periods about six-10,000 years years ago. 'That is my best guess,' [Eiberg] said. 'It could be the northern part of Afghanistan.'
Image source here.