What determines human eye color?

Human eye color is a polygenic phenotypic trait determined by the pigmentation of the iris and the scattering of light within its stroma. Melanin concentration and cellular density in the iris layers control brown shades, while structural color phenomena like Tyndall scattering create blue, green, and hazel appearances. As of 2010, up to 16 different genes, including OCA2 and HERC2, have been associated with its inheritance.

What we know

• Eye color is a polygenic phenotypic trait determined by iris pigmentation and the frequency-dependence of light scattering by the stroma's turbid medium. [1, 2]
• Iris pigmentation varies from light brown to black based on melanin concentration in the pigment epithelium and stroma, along with stromal cellular density. [2]
• Blue, green, and hazel eye appearances result from structural color via Tyndall scattering in the stroma, meaning no blue or green pigments are actually present. [2]
• As many as 16 genes, including OCA2 and HERC2, have been associated with the complicated inheritance of human eye color. [2]

Where to go next

• the bigger pictureHow do genes control inherited traits?
• a case in pointWhat causes diluted eye color in horses?
• how it workedHow does melanin concentration affect iris pigmentation?
• compared withHow does equine coat color inheritance work?
• whenWhen do mammals develop their permanent eye colors?
• an unexpected connectionWhy do horses have a gene that alters eye color without changing coat color?While eye color and coat color are frequently linked in animal genetics, the tiger-eye gene in horses uniquely affects eye shade independently of coat color.

Sources

• [1]eye color (Wikidata Q23786) · CC0 1.0
• [2]Eye color · CC BY-SA 4.0
• [3]Introduction to genetics · CC BY-SA 4.0
• [4]Tiger eye · CC BY-SA 4.0
• [5]Equine coat color · CC BY-SA 4.0