Why Do Some People Have Blue Eyes ?

People are fascinated by eye color. When I talk to expectant parents, it's fun to talk about the likelihood of their baby having brown, blue, or green eyes. When Nora was born, she, like many infants, had grayish-colored eyes. Some thought her eyes were blue, but I was pretty sure they would be brown like her mother's.

What causes specific people to have different eye color? Well, we've known for a long time that eye color is genetically based. Recently, however, a team at the University of Copenhagen team has identified the specific gene that determines if someone's eyes are going to be blue.

Professor Eiberg from the Department of Cellular and Molecular Medicine explained that “originally, we all had brown eyes. 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." It is estimated that this mutation occurred 6,000 to 10,000 years ago.

People who have brown eyes have a lot of a pigment called melanin in the iris. (This is the same pigment that gives some people darker skin color than others.) People with green eyes have less melanin in their irises than brown-eyed people, and people with blue eyes have the least amount of melanin.

Evidence now shows that all blue-eyed people have a common ancestor. The genes that control eye color have significant variation, but the gene responsible for blue eyes is much more specific. In the group studied, blue-eyed people had all inherited the same switch at exactly the same spot in their DNA.

This doesn't mean that anyone has any more control over whether their children are going to have blue eyes or not, but we do have a better understanding of why I have blue eyes, but my daughter does not.

Be Well!

Nathan Bonilla-Warford, OD
Bright Eyes Family Vision Care