Variations in multiple genes determine a person's eye color, according to Genetics Home Reference. Most of these genes produce, transport or store melanin, the pigment responsible for eye color. As of 2015, scientists think at least 16 genes are involved in determining eye color, explains the National Center for Families Learning.
Genes determine eye color primarily by controlling the amount of melanin produced and the location of melanin in the iris of the eye, states the National Center for Families Learning. People with blue eyes have very little melanin in the front layers of the iris. Brown-eyed people have abundant amounts of melanin in the iris.
The gene primarily responsible for determining eye color is OCA2, which is located on chromosome 15, according to Genetics Home Reference. OCA2 produces the P protein, which plays a role in the development of the cellular structures that make and store melanin. Also on chromosome 15, the HERC2 gene is responsible for activating the OCA2 gene, and thus is another significant gene related to eye color. Several other genes play a less significant role in determining eye color. The effects of these genes combine with the effects of OCA2 and HERC2 to produce a person's eye color.