Blue eyes are caused by a genetic mutation in the OCA2 and HERC2 genes. These genes are located on chromosome 15 and affect the production of melanin in the iris.  Explanation       OCA2     Controls the amount of pigment in the iris. A mutation in this gene limits the production of melanin, resulting in blue eyes.     HERC2     Helps turn on the OCA2 gene to produce pigment. A mutation in this gene prevents the OCA2 gene from working properly, resulting in blue eyes.