Eye Color Genetics

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Of the many physical characteristics expectant parents muse about, the color of their baby's eyes is arguably one of the most common. But although eye color is determined by genetics, it takes a year for a child's permanent eye color to develop.

A baby with large, blue eyes
 ePhotoAlto / Ale Ventura Collection / Brand X Pictures / Getty Images

It is common for parents to wonder why their bouncing blue-eyed baby is sporting hazel peepers as a toddler. During the first year of life, a baby's eye color will change as the eye takes on its permanent hue.

Understanding how eyes get their color and the role genetics play can take some of the mystery out of this phenomenon. And while eye color is mostly a matter of aesthetics, it sometimes can be an indication of certain health issues.

Scientists once believed eye color was determined by a single gene, but advances in genetic research and genomic mapping have revealed that more than a dozen genes influence eye color.

How Eye Color Develops

The colored part of the eye is the iris. What we perceive as eye color is a combination of pigments produced in a layer of the iris known as the stroma. There are three such pigments:

  • Melanin: The yellow-brown pigment that also determines skin tone
  • Pheomelanin: A red-orange pigment responsible for red hair that is predominant in green and hazel eyes
  • Eumelanin: A black-brown pigment that determines hue saturation and is abundant in dark eyes

The combination of pigments, as well as how densely they're dispersed and how they're absorbed by the stroma, determine whether an eye looks brown, hazel, green, gray, blue, or a variation of those colors.

For example, brown eyes have denser concentrations of melanin than green or hazel eyes. Interestingly, blue eyes have very little pigment and appear blue for the same reason the sky and water appear blue—by scattering light so that more blue light reflects back out. A complete absence of melanin results in the pale blue eyes of people with albinism. 

A newborn's eyes typically are dark and the hue often correlates to skin tone. Caucasian babies tend to be born with blue or grey eyes, while Black, Hispanic, and Asian babies commonly have brown or black eyes.

However, at birth pigment is not widely distributed in the iris. During the first six months of life, pigment epithelial cells start to pump melanin, pheomelanin, and eumelanin into the stroma. By age 1, eye color is usually set.


Eye color is determined by multiple variations of genes that direct the production and distribution of melanin, pheomelanin, and eumelanin. The predominant genes influencing eye color are OCA2 and HERC2, both located on human chromosome 15.

Each gene has two different versions (alleles)—one inherited from the mother and one inherited from the father. If the two alleles of a specific gene are different (heterozygous), what is known as a dominant trait is expressed. The unexpressed allele is recessive.

If a trait is recessive, like blue eyes, it generally only appears when the alleles are the same (homozygous).

Brown eye color is a dominant trait and blue eye color is a recessive trait. Green eye color is a mix of both. Green is recessive to brown but dominant to blue.

Predicting Eye Color

Without knowing precisely which genes a baby will have it's not possible to predict with total certainty what color their eyes will be, but there are ways to make fairly accurate predictions.

One of these is by using a simple grid chart called the Punnett square on which genetic traits of one parent are entered in the top rows of the grid and those of the other parent are entered in far-left columns. Plotting the contribution each parent makes provides a better-than-average probability of their offspring's eye color.

Determining each parent’s alleles can get a little complicated depending on the eye color. As a dominant trait, brown eyes can result from six different genetic combinations and can hide recessive traits of green or blue eye color. To factor in hidden (recessive) traits, it is helpful to know the grandparents' eye colors.

For example, a blue-eyed parent whose entire family has blue eyes and a brown-eyed parent whose mother and father were brown- and blue-eyed has a 50/50 chance of a blue-eyed or brown-eyed child.

Probability of Eye Color
Parent 1 Parent 2 Blue Green Brown
Blue Blue 99% 1% 0%
Blue Green 50% 50% 0%
Blue Brown 50% 0% 50%
Green Green 25% 75% 0%
Green Brown 12% 38% 50%
Brown Brown 19% 7% 75%

Scientists have begun to develop methods for predicting eye color using genetic tests that identify specific polymorphisms that can indicate how much melanin, pheomelanin, and eumelanin will be produced as well as the degree of pigment saturation in the iris.

Eye Color and Health

A baby's eye color may also reveal congenital diseases and other conditions. Babies whose eyes are different colors—known as heterochromia—may have Waardenburg syndrome, a genetic condition that can cause hearing loss in one or both ears. People with Waardenburg syndrome may also be born with very pale eyes or one eye that is two colors.

Very pale blue eyes may be caused by ocular albinism, in which there is a total absence of pigment in the iris. As an X-linked recessive disorder, ocular albinism occurs almost exclusively in men since they have two X chromosomes. (Women, who have an X and a Y chromosome, may be carriers.)

Studies suggest fewer than one out of every 60,000 men has ocular albinism.

A baby also may be born missing all or part of their iris, a genetic condition known as aniridia caused by mutations in the PAX6 gene, which plays a critical role in the formation of tissues and organs during embryonic development.

A Word From Verywell

While understanding the genetics of eye color can offer a probability of eye color, there are no certainties. If you have any questions about your child's eye color or overall eye health, bring your concerns to their pediatrician.

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