What is eye colour?

Eye color is a polygenic phenotypic character determined by two main factors: the amount of melanin in the iris's stromal layer and the scattering of light in the stroma. Eye color is usually classified as either brown, blue, green, or hazel. However, there are many variations and combinations of these colors, and eye color can change over time.

Melanin is a pigment that gives color to skin, hair, and eyes. The amount of melanin in the iris determines the darkness or lightness of the eye color. Brown eyes have a lot of melanin, blue eyes have very little melanin, and green eyes have a moderate amount of melanin.

The scattering of light in the stroma is another factor that determines eye color. The stroma is the connective tissue that makes up the bulk of the iris. When light hits the stroma, it is scattered in all directions. This scattering of light is what gives eyes their characteristic sparkle. The amount and type of scattering depend on the size, shape, and density of the collagen fibers in the stroma.

Eye color is a complex trait influenced by several genes and environmental factors. The exact genetic mechanisms that determine eye color are not fully understood, but it is known that several genes are involved. Some of these genes code for proteins that are involved in the production or transport of melanin. Other genes code for proteins that are involved in the scattering of light in the stroma.

Environmental factors, such as exposure to sunlight and age, can also affect eye color. Exposure to sunlight can cause the iris to become darker, and aging can cause the iris to become lighter.