Have you ever wondered why there’s wide variation in eye color among people or how these different colors come to be? Here’s a complete breakdown of the science behind eye color variations.
How is eye color created?
The colored part of our eye, the iris has 2 layers – the epithelium (front layer) and stroma (back layer). The variation occurs in the stroma.
The stroma contains collagen fibers and melanocytes (pigment-producing cells). The number of melanocytes depends on genetics and varies among people.
Furthermore, the pigments produced are of 2 types – eumelanin and pheomelanin whose concentrations varies among people according to genetics.
The combination of these factors along with the way light interacts with the iris structure determines whether a person has blue, green, brown, hazel or grey eyes.
The genetics behind
While many genes contribute to eye color, two genes on chromosome 15 play a key role– OCA2 and HERC2.
OCA2 gene produces a protein involved in building melanosomes (the tiny compartments where pigment is produced and stored). The more active the gene is, the more melanin the iris produces.
HERC2 gene controls the OCA2 gene – it’s variation influences OCA2 activity, reducing pigment production and resulting in lighter eyes.
Apart from these two, additional genes fine-tune the shades. This explains the wide spectrum of intermediate eye colors: steel blue, gray, green, hazel, amber and every shade in between.
Source: Why Do People Have Different Eye Colors? - ScienceInsights
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