Why do different people have a different eye color ?

Some people have different coloured eyes because of a condition known as heterochromia. This is caused by lack of or too much of a certain pigment in the entire iris or in part of it. It can be acquired through disease or when one gets an injury. The different eye colors are amber, blue, brown, gray, gren, hazel, red and violet.  

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Eye colororeye colouris apolygenicphenotypic characterdetermined by two distinct factors: thepigmentationof theeye'sirisand the frequency-dependence of thescatteringof light by theturbidmedium in thestroma of the iris.

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Eye colororeye colouris apolygenicphenotypic characterdetermined by two distinct factors: thepigmentationof theeye'siris[1][2]and the frequency-dependence of thescatteringof light by theturbidmedium in thestroma of the iris.

In humans, the pigmentation of the iris varies from light brown to black, depending on the concentration ofmelaninin theiris pigment epithelium(located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.[4]The appearance of blue and green, as well as hazel eyes, results from theRayleigh scatteringof light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky. Neither blue nor green pigments are ever present in the human iris or ocular fluid.Eye color is thus an instance ofstructural colorand varies depending on the lighting conditions, especially for lighter-colored eyes.

The brightly colored eyes of many bird species result from the presence of other pigments, such aspteridines,purines, andcarotenoids.[6]Humans and other animals have manyphenotypicvariations in eye color.[7]The genetics of eye color are complicated, and color is determined by multiple genes. So far, as many as 15 genes have been associated with eye color inheritance. Some of the eye-color genes includeOCA2andHERC2.[8]The once-held view that blue eye color is a simplerecessive traithas been shown to be incorrect. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.[9][10]However,OCA2gene polymorphism, close to proximal5′regulatory region, explains most human eye-color variation.

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