Different Eye Colors

Eye color is a genetic trait inherited from parents, but it is actually a polygenic trait, meaning multiple genes combine to determine eye color. The amount of melanin in the eye, also an inherited trait, is the final determinant of eye color. Irises that are melanin rich will yield brown eyes while irises with little melanin will yield blue eyes. When each iris has different amounts of melanin, the result is two different colored eyes.

Having different colored eyes is a condition is more commonly seen in cats, dogs and horses, rather than humans. It is believed that an alteration in one of the genes controlling eye color produces the condition, but melanin is not the only cause. A genetic disorder called Waardenburg Syndrome, which commonly results in a person being deaf or albino, is also associated with an individual having different colored eyes.

Changes in the color of one or both eyes can also be the result of injury, hemorrhage, or glaucoma. Pigmentary glaucoma, neurofibromatosis and neuroblastoma are also diseases that also can cause eye colors to differ.

Resources:

Learn more about heterochromia, the medical term for different colored eyes. This Web site lists causes for the condition and provides guidelines about when patients with the condition should see a healthcare provider.

Scientific American provides a detailed technical explanation of why a person might have eyes of two different colors.

Learn how traits are passed from one generation to the next through DNA.

November 1, 2003