Tuesday, August 18, 2009
What is Eye Color?
It may be man's most attention-grabbing quality, but what really is eye color?
In short, eye color is the expression of a combined number of genes. Eye color expression is like screwing in a certain color light bulb to emit a certain color of light. If you replace the bulb with a bulb of another color, the emitted light's color will change.
Eye color is not a blend of the parents' colors. Each parent has two pairs of genes on each chromosome, all of which can effect the ultimate color expression in a myriad of ways. Brown eye color is the dominant gene, needing only one copy to be expressed, while blue (recessive) requires both copy's. However, no one gene controls eye color - the OCA2 gene, controlling the amount of melanin pigment produced, accounts for ~74% of variation in eye color. Other genes effect the OCA2 gene's expression.
Geneticist Dr Rick Sturm states, "We believe ... there are two major genes - one that controls for brown or blue, and one that controls for green or hazel - and others that modify this trait". This means that brown-eyed parents can have a blue-eyed child, and vice versa.