How Genetics Determine Baby's Eye Color

What determines a baby's eye color?

Eye color is determined by genetics. The color of your eyes, whether blue, brown, hazel, or green, is ultimately the result of multiple genes. In general, children inherit their eye color from their parents, a combination of the eye colors of Mom and Dad. A baby's eye color is determined by the parents' eye color and whether the parents' genes are dominant genes or recessive genes.

Blue-eyed vs. brown-eyed

While it's unusual, it is possible for blue-eyed parents to have a brown-eyed child. Brown and maybe green are considered dominant, but even two browns can make a blue-eyed baby because there are no full 100 percent definite rules, so you can only go by a percent.

If both of you have brown eyes, then there is generally a 25% chance that the baby will have blue eyes if both of you carry the recessive blue-eye gene. But if only one of you has a recessive blue-eye gene, and the other has two brown, dominant genes, then there is a less than 1% chance of the baby having blue eyes. 

How do the genes work together?

Keep in mind that inheritance of eye color isn't exactly simple because it is polygenic, meaning that the trait is influenced not by one gene, but by multiple genes working together. Even if only the most obvious gene is considered — the one with the most control over brown vs. all other eye colors, there are still a few things to consider.

— the parents' eye colors — whether the parents are homozygous or heterozygous for that color — if the eye colors of the parents are dominant or recessive.

What is gene dominance?

A dominance of one copy of the gene over the other means that the dominant copy has an effect you can see, in this case, you can see that the person has brown eyes. Brown (and sometimes green) is considered dominant. So a brown-eyed person may carry both a brown version and a non-brown version of the gene, and either copy may be passed to his children. 

Eye Colors Worldwide

Brown is the most common eye color in the world with between 55% and 79% of the people of the world having brown eyes.13 Blue and green eyes are genetically recessive, so they are far less common. Less than 10% of the world's population is believed to have blue eyes, while only around 2% has green eyes.14

Hazel and amber eyes are also uncommon. Roughly 5% to 8% of people will have hazel-colored eyes. Amber eyes (caused when pheomelanin dominates the iris) is extremely rare, manifesting in less than 1% of people.

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