The Genetics of Baby Eye Color: What Science Actually Knows (and a Tool to See for Yourself)
Eye color inheritance is more complex than what you learned in biology class. Here’s what the research shows, and a free calculator that uses it.
If you took high school biology, you probably learned that eye color is simple: brown is dominant, blue is recessive, two blue-eyed parents can’t have a brown-eyed child. Punnett square, case closed.
A Punnett Square is a simple graphical grid used in biology to predict the potential genetic outcomes (genotypes and phenotypes) of offspring from a cross between two parents with known genotypes. Developed by Reginald C. Punnett in 1905, this tool visually represents Mendelian inheritance by combining maternal and paternal alleles to calculate probabilities for offspring traits.
That model is wrong.
It is so wrong, in fact, that geneticists have spent the past two decades dismantling it. Eye color in humans is not determined by a single gene with two alleles.
It is a polygenic trait influenced by at least 16 genes, with the primary control sitting on chromosome 15 in a region involving two genes called OCA2 and HERC2.
The interaction between these genes, along with modifiers on at least five other chromosomes, produces the full spectrum of human iris color: from the palest gray through blue, green, hazel, amber, and the deepest brown.
Two blue-eyed parents can, in fact, have a brown-eyed child. It is uncommon. But it happens, and the genetics explain why.
Read on as paying subscriber…. And access the eye color tool
