Ever wondered if a child’s eye color can be predicted? Or how two brown-eyed parents can have a blue-eyed child? Or why an albino’s eyes are pink? How we inherit eye color is a fascinating example of genes at work. Read on to learn the answers to these questions and more about eye color and genetics.
Why are eyes different colors?
Eye color is determined by the amount of a pigment called melanin in the iris. The more pigment, the darker the eye. There are no blue or green pigments in the eye. Lighter eye colors are due to an effect of light scattering in the stroma (a layer of the iris) called Rayleigh scattering, similar to why the sky looks blue. Many babies of European descent are born with blue eyes that change to brown because melanin production has not begun at the time of birth.
Can eye color be predicted?
Yes and no. Eye color probability can be determined, but what color a child’s eyes will be often can be impossible to predict exactly. Even in the case of two blue-eyed parents, it may be almost certain they would have a blue-eyed child, but because eye color is influenced by multiple genes, it is possible for a blue-eyed couple to have a brown-eyed child. While there is evidence that up to 16 genes can influence eye color, the two most important genes are OCA2 and HERC2. These genes come in two different versions, or alleles. If the two alleles are different, only one is expressed and is called dominant while the unexpressed one is called recessive. In the case of eyes, brown is dominant to green and green is dominant to blue, so blue eyes only occur when all four alleles are blue. A way of predicting the color of a child’s eyes is to input the parents’ eye colors into a graph called a Punnett square. By plotting the various combinations of alleles in this graph, the odds of eye color options can be calculated. For example, if both parents have brown eyes, but are carriers of a blue gene, according to all the potential combinations using a 2-gene model, the child will most likely have brown eyes, but has a one in four chance of having blue eyes. If you’re curious about what color eyes your children might have, here’s an online predictor that does all the calculating for you.
Unusual eye colors
You may have seen someone with pink or violet eyes, or maybe someone with one blue and one brown eye. True pink, red, or violet eyes are due to albinism, a condition in which the body is unable to produce or distribute melanin. The pink color is the color of the retina showing through. Heterochromia is a condition in which the color of one iris is different or partially different from the other eye. This is due to uneven melanin content caused by genetics or injury.
Our eyes are the most expressive parts of our body, and their color is one of our most distinguishing characteristics. While it may be impossible to permenantly change your eye color, it’s simple enough to try a new look temporarily with colored contacts. A good example of these kinds of lenses are CooperVison’s Expressions color contacts. Even if you have perfect 20/20 vision and just want to try contacts for the color, it’s very important to see an eye care professional and be properly fitted.