Eye color is a complicated genetic trait set by how genes from each parent are paired. Researchers used to think that eye color was controlled by just one gene, but new genetic studies have shown that more than 50 genes are involved.
What color a baby’s eyes are depends on how much and what kind of melanin is stored in the iris. Even though eye color is mostly just a matter of looks, it can sometimes mean the baby is sick.
This page discusses genes that affect eye color. It explains how genes cause different mixes of pigments that decide what color eyes your baby will have.
How Eye Color Grows
The iris is the name for the colored part of the eye. The colors in our eyes are made up of pigments, which are colors that are made in the stroma, a layer of the lens. This kind of color comes in three forms:
- The color of skin is controlled by melanin, a yellow-brown pigment.
- Red hair is caused by a pigment naming pheomelanin, which is red-orange. People with green or brown eyes are more likely to have it.
- Many dark eyes have a pigment called eumelanin, which is black-brown. It decides how bright the color will be.
What makes an eye look brown, hazel, green, gray, blue, or a mix of those colors is its pigments and how well the stroma absorbs and spreads them out.
One example is that brown eyes have more melanin than green or hazel eyes. Blue eyes don’t have much color. The same thing that makes the sky and ocean blue also makes them blue: they scatter light so that more blue light bounces back out.
People with albinism have ashen blue eyes because they don’t have any melanin.
Baby Eye Color
A baby’s eyes are usually dark, and the color is often linked to the color of their face. Blue or gray eyes are familiar in white kids when they are born. Babies who are black, Hispanic, or Asian often have brown or black eyes.
If your child is born with blue eyes, they might change color. When the eye is first born, the color is not spread out evenly in the iris. More of the colors are made in the first six months of life. By age 1, your eyes generally stay the same color.
Trying To Guess Eye Color
It’s hard to say what color a baby’s eyes will be without knowing exactly which genes they will have. But there are ways to guess what will happen pretty well.
One way is to use the Punnett square, a simple grid chart. The traits of one parent are typed into the first few rows of the grid. In the far left columns, you put the genetic characteristics of the other parent.
If you plot the effect that each parent has, you can get a better-than-average idea of what color their child’s eyes will be.
Still, the Punnett square chart could be better; it can’t accurately predict more complicated transfer problems. For instance, the Punnett square says that two people with blue eyes can’t have a child with brown eyes.
But if the parents with blue eyes have DNA for brown eyes from a parent, then it is still possible—though not likely—that their child will have brown eyes.
Depending on eye color, it can be hard to figure out which parent’s genes are which. Brown eyes can be caused by six different sets of genes as a dominant trait.
They can also hide traits that make your eyes green or blue. Knowing what color your grandparents’ eyes are helps if you want to find any genetic traits.
A parent with blue eyes whose whole family has blue eyes and a parent with brown eyes whose mother and father were both brown and blue-eyed have an equal chance of having a child with blue or brown eyes.
Eye Health And Color
The color of a baby’s eyes may also show if they have genetic diseases or other health problems.
The Waardenburg Syndrome
People with Waardenburg syndrome may have heterochromatic eyes. One blue eye and one brown eye are common signs of heterochromia.
People with Waardenburg syndrome may lose hearing in one or both ears. They may also be born with very pale eyes or one eye that is two different colors.
Various colors in the same eye, known as central heterochromia or “tie-dye eyes,” are not linked to health issues.
Albinism Of The Eyes
One sign of ocular albinism is having very pale blue eyes. In this case, there is no color at all in the eye.
Because it is an X-linked recessive disorder, ocular albinism mostly affects guys. Men have one X chromosome and one Y chromosome.
That sickness has a gene on the X chromosome. So, even though it’s recessive, the gene for the condition will be turned on in guys.
Conversely, women may be carriers because they have two X genes. They may have a gene for ocular albinism hidden by a regular gene. So, even if they don’t have the disease, they may be able to pass it on.
Studies show that ocular albinism affects less than one in every 60,000 guys.
Having Aniridia
A baby may also be born without all or part of their iris. This is called aniridia and is caused by genes.
If you have aniridia, it means that both eyes are affected simultaneously. The disease makes the pupil look a lot bigger and shaped differently.
People with aniridia have trouble changing to light, making their vision blurry and sensitive to light.17
Changes in the PAX6 gene lead to aniridia. During the early stages of growth, this gene is very important for making tissues and organs.17
Your baby’s eye color is determined by his or her genes. The pigments that makeup eye color are made in the stroma. Brown eyes have more melanin than from the green or hazel eyes, and blue eyes have little color.
Which pigments are made and the baby’s eye color depends on the mix of genes they get from each parent. These genes can also cause some diseases.
Read More: The Purpose Of Eyebrows And Eyelashes