New research shows that people with blue eyes share a common ancestor. A research team at the University of Copenhagen has identified a gene mutation that occurred between 6,000 to 10,000 years ago, which is responsible for the eye color of all blue-eyed individuals living on the planet today.
What is a Gene Mutation?
Professor Hans Eiberg from the Department of Cell and Molecular Medicine explains: “Originally, all of us had brown eyes, but a genetic mutation affecting the OCA2 gene in our chromosomes led to the creation of a ‘switch’ that can ‘turn off the ability to produce brown eyes.’”
Blue-eyed individuals have only a small degree of change in the amount of pigment in their eyes.
The OCA2 gene encodes for a protein known as P, which is involved in the production of melanin, the pigment that gives color to our hair, eyes, and skin. However, the ‘switch’ located in a gene adjacent to OCA2 does not completely turn off the gene; instead, it restricts its activity, reducing melanin production in the iris—effectively ‘diluting’ brown eyes to blue. Therefore, the effect of the switch on OCA2 is very specific. If the OCA2 gene had been completely destroyed or turned off, the result would be different.
Limited Genetic Variation
The change in eye color from brown to blue can be explained by the amount of pigment in the iris, but blue-eyed individuals exhibit only a small degree of change in their eye pigment. Professor Eiberg states: “From this, we can conclude that all blue-eyed individuals are related to the same ancestor. They all inherited the same switch at the same location in their DNA.” In contrast, brown-eyed individuals show significant individual variation in the DNA region controlling their melanin production.
Professor Eiberg and his team examined mitochondrial DNA and compared the eye colors of blue-eyed individuals from diverse countries such as Jordan, Denmark, and Turkey. His findings are the latest discovery in a decade of research on the gene, which began in 1996 when Professor Eiberg first suggested that the OCA2 gene was responsible for eye color.
Nature Shuffles Our Genes
The mutation from brown to blue eyes is neither a positive nor a negative mutation. It is one of several mutations, such as hair color, baldness, freckles, and beauty spots, that do not increase or decrease human survival chances. As Professor Eiberg puts it: “It simply shows that nature is continuously shuffling the human gene pool, creating a genetic mix of human chromosomes and trying out different changes like these.”
