Have you ever wondered why some people have brown eyes while others have blue? Well, it turns out those beautiful blue eyes are actually a result of genetic mutation which can be traced back to one common ancestor.
A team of researchers at the University of Copenhagen have traced the genetic mutation, which they estimate could have taken place over 6-10,000 years ago. Ultimately they discovered that this single mutation has caused every single case of blue eyes that have come after it.
Professor Hans Eiberg, from the Department of Cellular and Molecular Medicine, and his team of researchers examined mitochondrial DNA to compare the colour of blue-eyed people in diverse countries like Jordan, Denmark and Turkey.
He spoke to Science Daily about genetic mutation and how it occurred, “Originally, we all had brown eyes,” he said.
“But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch,” which literally “turned off” the ability to produce brown eyes.”
The OCA2 gene he refers to codes for the P protein, which is involved in producing melanin, the pigment that gives our hair, eyes and skin colour. Turning off the “switch” to the gene adjacent to this essentially dilutes brown eyes to blue. If the OCA2 gene itself had been completely destroyed or turned off we would be without melanin in our hair, skin and eyes – known as albinism.
You may be wondering, how is this any different from green eyes? Well, according to the research green eyes can be explained by the amount of melanin in the iris, whereas blue eyes only have a small amount of variation in melanin in their eyes. Those with brown eyes have a larger individual variation in the area of their DNA that controls the production of melanin.
“They [blue-eyed people] have all inherited the same switch at exactly the same spot in their DNA,” Professor Eiberg said. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor.”
Professor Eiberg first found the OCA2 gene was responsible for eye colour in 1996.
He says that the blue eye mutation is neither positive nor negative but one of several mutations, like hair colour, freckles and beauty spots, which will not increase or reduce a humans chance for survival.
“It simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”