What Determines Eye Color?

Our eye color is something that is written into our DNA, predetermined before we are even born! It is determined by the genes that we receive from our parents. We receive an allele from each parent. It isn’t as simple as you think, though. Children can have totally different colored eyes than their parents. Eleven different genes control eye color which is why there are so many variations.

Dominant and Recessive

Alleles determine how a certain trait will look on a certain person. These can be either dominant or recessive. If both alleles are the exact same, called homogenous, that same characteristic will manifest itself. So, if you get a brown eye allele from both parents, you will have brown eyes. If the alleles are heterozygous, or different, whichever one is dominant will be the one that is manifested. For example, brown is dominant over blue, so if you receive one blue allele and one brown allele, the brown eyes will be manifested. But since you still have the recessive blue allele that can still be passed on to your children which is why brown eyed parents can still end up with blue eyed children. Crazy!

What makes eye color look different?

It’s all in the melanin! Melanin is a pigment that is found in the skin as well as the eyes. There are two different types of melanin- eumelanin which is brown-black and pheomelanin which is red. The more melanin, the darker the eye and vice versa. The iris (the colored part of the eye) has two layers. Most people have melanin in the back layer. The amount of melanin in the front layer will determine the color of your eyes. Brown eyes have the most, green has less then brown, and blue has no melanin. Albino
eyes have no melanin in either layer! Eye colors that fall between dark brown and light blue have varying amounts of pigment and some areas without pigment which leads to more unique colors. There are also different patterns on our iris that make our eyes unique as well.

Which eye colors are the most common?

Blue or grey eyes are in about 1/3 of the population. Dark brown eyes are the next most common, in about 25% of the population. Lighter brown makes up 16%. Overall, brown is more common than blue, and green is the most rare. In different parts of the world, certain eye colors are more common. In Ireland, green is more common than the rest of the world. It is so amazing that only two types of pigment, eumelanin and pheomelanin, can give us so many unique colors. I have seen plenty of eyes in my career and none are exactly the same!

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