How do you get color in an eye?

Answer 1

Eye colours can range from the most common colour, brown, to the least common, green. Rare genetic mutations can even lead to unusual eye colours: black, red, or the appearance of violet. Eye colour is an inherited trait influenced by more than one gene.[9][10] These genes are being sought using associations to small changes in the genes themselves and in neighboring genes. These changes are known as single nucleotide polymorphisms or SNPs. The actual number of genes that contribute to eye color is currently unknown, but there are a few likely candidates. A study in 2009 found that it was possible to predict the color of eyes in Rotterdam with more than 90% accuracy for brown and blue, using just six SNPs (from six genes). [11] The gene OCA2 (OMIM: 203200), when in a variant form the gene causes the pink eye color and hypopigmentation common in human albinism. (The name of the gene is derived from the disorder it causes, oculocutaneous albinism type II.) Different SNPs within OCA2 are strongly associated with blue and green eyes as well as variations in freckling, mole counts, hair and skin tone. The polymorphisms may be in anOCA2 regulatory sequence, where they may influence the expression of the gene product, which in turn affects pigmentation.[8] A specific mutation within the HERC2 gene, a gene that regulates OCA2 expression, is partly responsible for blue eyes.[12] Other genes implicated in eye color variation are: SLC24A4 [13] and TYR.[13] Blue eyes with a brown spot, green eyes and gray eyes are caused by an entirely different part of the genome. As Eiberg said: "The SNP rs12913832 [of the Herc2 gene] is found to be associated with the brown and blue eye color, but this single DNA variation cannot explain all the brown eye color variation from dark brown over hazel to blue eyes with brown spots."

Source: Wikipedia