Eye colour depends on the relative abundance of two kinds of melanin pigments – eumelanin and pheomelanin in the iris. In brown eyes (some appear black but are actually brown), absolute melanin content is high and eumelanin predominates. A higher relative abundance of pheomelanin and lower absolute melanin content overall are found in blue or green irises.
Eye colour was once thought to be a strictly mendalian trait determined by two genes (alleles), one each for brown and blue colour, with brown dominant over blue. Several new genes were reported starting in 2008 taking the total number closer to 11. Now, a Genome-wide association study has discovered 50 novel genes coding for eye colour.
The largest eye colour GWAS (Genome-wide association study) to date involved 192,986 European participants from 10 populations and 1636 Asian participants (Han Chinese and Indian ancestry). Eight of the newly discovered genes were known to code for hair and skin colour.
The study by an international group of (45+) researchers highlights the immense genetic complexity of human eye colour.
Read more about the study here.
