Genetics, explained simply

How eye color is inherited

Forget the two-allele Punnett square. Eye color comes from melanin, light and dozens of genetic regions, which is why it forms a spectrum and not a set of neat boxes.

Sources checked November 2026

01: The ingredients

Pigment first, physics second

Eumelanin

The brown-black pigment. The more eumelanin in the iris's front layer, the browner the eye. Blue irises have very little pigment of any kind.

Pheomelanin

The red-yellow form of melanin, also found in red hair. A 1998 study linked it to green irises. Popular guides often use the older term lipochrome.

Light scattering

When the front of the iris has little melanin, light scatters and the blue end of the spectrum reflects back out. Blue eyes get their color this way, not from a blue pigment.

02: The genetics

Dozens of regions, two stars

A 2021 study of almost 195,000 people is the largest so far. A few genes matter most, and the rest nudge the shade. Together, common variants explain about 53% of eye color differences, so a large part is still unexplained.

Gene / locus	Role	Influence
OCA2	Makes the P protein, which helps melanosomes (the cells' pigment structures) mature. A major contributor to the brown–blue spectrum.	Major
HERC2	Contains a regulatory variant (rs12913832) that lowers OCA2 activity like a dimmer switch. This is the best-known variant behind blue eyes.	Major regulator
ASIP, IRF4, TYR	Named by MedlinePlus among the other genes that contribute. They adjust melanin and also influence hair and skin color.	Moderate
61 genomic regions	A 2021 Science Advances study of almost 195,000 people found 124 signals in 61 regions, 50 of them new. Some affect pigment, and others affect the structure of the iris.	Fine-tuning

Inheritance is probability, not destiny

Two brown-eyed parents usually have brown-eyed children, but can have blue or green ones if both carry variants that lower melanin. Two blue-eyed parents usually have blue-eyed children, but MedlinePlus confirms that brown is possible, though uncommon. Eye color can't prove paternity.

Read the full explainer

Newborn eyes are a draft

Not all babies are born with blue eyes. In one study of 192 newborns, 63% had brown eyes and 20.8% had blue. Melanin builds after birth, so light eyes can darken, and color tends to settle by about age 6. Eye color predictions for babies are rough guesses at best.

In adults, slow change can happen, but a sudden change, or a change in one eye only, needs a visit to an eye doctor. See our disclaimer.

03: Questions

Genetics FAQs

Is eye color really not a simple dominant or recessive trait?

Correct. The 'brown beats blue' model taught in schools is a simplification. Eye color is polygenic, with many genes contributing, which is why siblings with the same parents can have different eye colors.

Can two blue-eyed parents have a brown-eyed child?

Yes, though it is uncommon. MedlinePlus Genetics confirms it. The parents may have blue eyes for different genetic reasons, and other genes can push melanin back up in a child.

Why do some babies' eyes change color?

Melanin in the iris builds after birth, so light eyes can darken. Eye color tends to settle by about age 6. Not all babies start with blue eyes: in one study of 192 newborns, 63% had brown eyes.

Are there genes for green eyes or gray eyes?

Not single ones. Green sits on a spectrum made by many variants, mostly the same genes involved in blue and brown. For gray, geneticists say the exact genes have not been identified.

Can eye color predict anything about health?

Only weakly, and only as a population pattern. A 2014 review linked darker irises to more age-related cataract, and lighter irises to a higher risk of uveal melanoma. It found no consistent link with macular degeneration.