Eye color is one of the most visible hereditary traits that has long attracted scientific interest. Despite its simple outward appearance, eye color determination depends on a complex interaction among multiple genes that regulate the production and distribution of the pigment melanin within the iris. The iris is the colored part of the eye and controls the amount of light entering through the pupil. Its color is determined by: • The amount of melanin present in its anterior layer. • The type of melanin (dark eumelanin or lighter pheomelanin). • The way light is scattered within its tissues. The greater the amount of melanin, the darker the eye color (dark brown). The lower the melanin concentration, the lighter the eye color appears (blue or green). The Genetic Basis of Eye Color It was once believed that eye color was controlled by a single gene following a simple dominant/recessive inheritance pattern. However, modern research has shown that the matter is far more complex. The most important genes associated with eye color are: • OCA2: regulates the production of melanin. • HERC2: controls the activity of the OCA2 gene. Both genes are located on chromosome 15. Variations in their DNA sequences result in differences in the amount of pigment produced. How Does Variation Occur? • A specific mutation in a regulatory region of HERC2 reduces the activity of OCA2. • Reduced OCA2 activity leads to lower melanin production. • Lower melanin levels result in lighter eye colors, such as blue. Environmental Factors and Changes with Age • Most light-skinned infants are born with light-colored eyes, and melanin production increases during the first year of life. • Certain diseases or mutations may alter eye color. • A rare condition called heterochromia occurs when the two irises differ in color. Eye color is a clear example of the complexity of human inheritance, as multiple genes interact to regulate melanin production within the iris. The simple rule that “brown is dominant and blue is recessive” is no longer sufficient to explain real variation. Advances in molecular genetics have revealed a precise regulatory network that governs this distinctive visible trait. University of Al-Mustaqbal – The First and Leading Private University