the view that blue eye colour is a simple recessive trait is incorrect. two main gene loci code for the eye pigment: "oca2" and "herc2". they sit next to each other on chromosome 15. mutations (snps) to these genes account for much of the variation seen in eye colour. "oca2" mutations close to the 5′ regulatory region explain most human eye-color variation. an intron in "herc2" contains the promoter region for "oca2", affecting its expression.