What color eye is most common?
December 16, 2006 2:00pm CST
Brown is one of the most common eye colors and, in many populations, it is the only iris color present. Eye color is an inherited trait influenced by more than one gene. In humans, three genes coding for eye color are currently known: EYCL1, EYCL2, and EYCL3. These genes account for three phenotypic eye colors (brown, green, and blue) in humans. Although it was once thought that brown eye color was always dominant and blue eye color was always recessive, the fact that two blue-eyed parents can give birth to a brown-eyed child has shown that the determination of eye color does not follow the simple rules of Mendelian inheritance, although this is so rare that scientists didn't even notice that it happens (perhaps 1 in 100,000,000) until recently. Eye color or eye colour is a polygenic trait and is determined primarily by the amount and type of pigments present in the eye's iris. Humans and other animals have many phenotypic variations in eye color. In humans, these variations in color are attributed to varying ratios of the two types of melanin produced by melanocytes in the iris: eumelanin and pheomelanin. The brightly colored eyes of many bird species are largely determined by other pigments, such as pteridines, purines, and carotenoids. Three main elements within the iris contribute to its color: the melanin content of the iris pigment epithelium, the melanin content within the iris stroma, and the cellular density of the iris stroma. In eyes of all colors, the iris pigment epithelium contains the black pigment, eumelanin. Color variations among different irises are typically attributed to the melanin content within the iris stroma. The density of cells within the stroma affects how much light is absorbed by the underlying pigment epithelium.