eye color

Eye color is one of the complex genetic characteristics (called "polygenic" that defies simple Mendelean genetic patterns because multiple genes contribute. Different eye colors result from varying ratios of the two types of melanin pigment produced in the iris: eumelanin (brown/black pigment) and pheomelanin (pink/red pigment).

But recent research indicates that as much as 3/4 of the variation in human eye color comes down to 3 nucleotides of a single gene, making eye color far more simple of a genetic trait than once thought.

As reported in the American Journal of Human Genetics, and summarized in the News and Views of the November 30th, 2006 issue of Nature, a particular region of the OCA2 gene explains ths three-quarters of the variation in human eye colour, and they have found that three single-nucleotide changes in this gene are strongly associated with having blue eyes. This data came from twin studies from 3,839 twins and their family members. OCA2 is the "oculocutaneous albinism II" gene which codes for a protein called "P protein" which in some as yet undetermined way regulates the production of pigment in melanocytes, thus affecting skin and eye color.