Eye color is a phenotype, an observable characteristic. Basically, it is the result of yellow and black melanin pigments in the eye’s iris. Eyes are not simply blue, green and brown. Other colors include gray, hazel, violet, red and amber.
The Genes of Eye Color
Mendel’s laws suggest that brown eyes are a result of a dominant trait, and blue eyes, a recessive trait. For example, if a father had blue eyes and a mother had brown eyes, their children would be more likely to have brown eyes. There is some truth in this linear model, but it is not always correct.
Eye color is polygenic, meaning several genes are involved. The current understanding of eye color suggests three genes are definitely in play:
- OCA2 (also referred to as bey2), on chromosome 15
- Bey1, on chromosome 15
- Gey, on chromosome 19
It is very likely that other genes are involved as well, which suggests predicting eye color is much more difficult than was once thought.
Blue-Eyed Parents Can Have Brown-Eyed Children
While blue eyed parents usually have blue-eyed offspring, they can have children with eye colors other than blue. Possible reasons for this include mutations and/or other genes. Although this area isn’t well understood, it should not be dismissed, particularly not by those in educating roles.
Eye Color Changes in Childhood and Adulthood
Newborns usually have blue eyes, and by the age of 3, their eye color will have fully developed. Eye color can change in adulthood due to environmental factors such as disease or medication. An adult experiencing a change in eye color should consult with a physician to determine if intervention is required.
Getting a Rough Estimate of Eye Color
The best way to predict eye color is to note down the eye colors of:
- Both of the potential parents
- The full siblings of the potential parents
- The mother and father of both potential parents
This can then be entered into an eye color calculator, such as provided by The Tech website. It’s important to keep in mind that this model uses a two gene model, therefore it can only give a rough estimate of eye color. Read Eye Color Genetics for more information on how eye color is inherited.
Sources
"Eye color: portals into pigmentation genes and ancestry", TRENDS in Genetics, published: August 2004, authors: Sturm, R.A and Frudakis, T.N.
"Sequences Association with Human Iris Pigmentation", Genetics, published: December 2003, Frudakis, T et al.
"How is Eye Color Determined?", The Tech website, accessed: November 23rd 2008, no author specified.
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