Blue-eyed? Thank a genetic switch that turns off your body’s ability to make brown pigment in your peepers. Researchers have finally located the mutation that causes blue eyes, and the findings suggest that all blue-eyed humans share a single common ancestor born 6000 to 10,000 years ago. Researchers have implicated the OCA2 gene in several eye colors. The gene is involved in the production of melanin, a pigment that gives hair and skin their hues. It also codes for brown eyes and can lead to green or hazel eyes when mutated. Despite years of searching, however, scientists have not found a mutation for blue eyes on the gene.
It turns out they were looking in the wrong place. Trying to narrow the site of the mutation, gene mapper Hans Eiberg of the University of Copenhagen and colleagues examined members of a large Danish family, an approach that allowed them to follow DNA as it passed from one generation to another. Then, by comparing people with brown or blue eyes, including people from Jordan and Turkey, the researchers were able to pinpoint the exact mutation. It wasn’t on the OCA gene but rather on a nearby gene called HERC2. The mutation works like a switch that regulates the OCA gene, the team reports in the January issue of Human Genetics, turning off the production of brown eye color and allowing blue eyes to shine through. Because blue eye color is found almost exclusively in people of European descent, Eiberg’s team speculates that the mutation traces back to the Neolithic expansion, when people in the Black Sea region migrated to northern Europe 6000 to 10,000 years ago.