People with this color of eyes have more than just iris pigmentation in common.
Eye color is determined by the genes of the parents. Brown is the most common color, while 8 to 10% of people have blue eyes. This color is associated with a recessive gene, which means that you have to inherit the rarest combination of genes from the parents for the color to truly become apparent. According to a study who analyzed the genetic data of about 800 blue-eyed people from around the world, they have more than just their eye color in common.
The researchers, scientists from the University of Copenhagen, focused on the OCA2 gene, which determines the level of brown pigment in the eye. They discovered that the genetic mutation that causes the blue color comes from a different gene, HERC2, which affects the presence of OCA2 and limits its ability to produce brown eyes.
The authors of the study then highlighted that 99.5% of the participants had undergone the same genetic mutation at the DNA level, which affected the production and expression of melanin, the molecule that gives the color of the iris. “They all inherited the same switch in exactly the same place in their DNA,” explained Professor Hans Eiberg of the Department of Molecular Medicine at the University of Copenhagen.
For the researchers, this common mutation would then come from a single individual: “We can conclude that all individuals with blue eyes are linked to the same ancestor,” explained the lead author of the study. He would have been born with a spontaneous mutation that would have then spread.
This “founding” genetic mutation that gave rise to this physical trait could have occurred between 6,000 and 10,000 years ago. To date, the first clearly identified person with blue eyes dates back to a 7,000-year-old skeleton. “Originally, we all had brown eyes,” the specialist said. In addition, the variations in shades of blue are less significant than those for brown eyes and this could indicate that the color blue appeared more recently. The reason for the original mutation, however, remains a mystery.