I’ve done blog posts on eye color in the past. However, I’ve never done one on the factors of eye color. So, up until 10 years ago or so, I thought I had brown eyes. My dad has brown eyes. My mom has blue. My sister has blue. Most of my first cousins on my mom’s side have blue. My father’s eye color cannot be mistaken for hazel, they are absolutely a dark brown. However, his father was a redhead with blue eyes. And since my sister has blue, Dad obviously carried the gene for it.
In high school, I learned brown is the dominant eye color and two people with blue eyes can’t have a brown eyed child. That was the 1990s. In the last few years, I’ve learned eye color isn’t that straight forward. And this misunderstanding of genetics is probably why I thought I had brown eyes for so long. I mean, they obviously weren’t blue. Meaning I had to get Dad’s brown eyes gene. Except, my eyes are indeed hazel, not brown.
My best friend, who is also my first cousin on my mom’s side, has grey-blue eyes. And like most of my mom’s family, she can get a sunburn from thinking about going outside. What does getting a sunburn have to do with blue or brown eyes, you ask? Melanin.
I have an olive tint to my skin. As a result, I can’t wear yellow, it makes me look like I have jaundice. I also have trouble with some other pastels. But when you put me in a rich jewel tone green, my eyes reflect a green color. Dark earth tones like hunter green and brown, make my eyes a dark rich brown color.
Recently, I was researching eye color. Because I shouldn’t be able to have hazel eyes. I should have brown or blue. And that’s where I learned that melanin plays a huge factor in eye color and may contribute to my hazel eye color.
Melanin is pigment in the human body. It’s what keeps us from getting sunburned and creates skin tones. People of African descent tend to carry genes for more melanin in their skin and their eyes. It’s why most people from Africa have brown eyes. The only part of the eye that has color is the iris and everybody on the planet has the same color in their iris “brown,” because that is the color of melanin. The lighter the color, the less melanin in the iris, the more likely the color being reflected back is on the blue wavelength spectrum. We aren’t seeing actual blue pigment, we are seeing the reflection of the blue light spectrum due to a lack of melanin.
The same is true of green eyes as it is of blue. Hazel is a bit different though. Hazel colored eyes have less melanin than brown eyes and more melanin than blue or green eyes. But they are caused not just by the overall amount of melanin in the iris, but the placement of it. Hazel eyes appear to change color when light hits them from a different angle. Often times, in hazel eyes, the melanin is concentrated near the pupil and as the pupil contracts and dilates, the visual appearance of the color changes as the melanin shifts locations, thereby changing the color of the eye.
The same is true of my best friend. Her grey eyes can appear a stormy grey or a dark blue, depending on how the light is reflected off her iris. These color changing effects are more common in people who carry different coloration genes for their eyes. Furthermore, while we used to think brown was always dominate, we’ve learned they aren’t and about 1% of all babies born to 2 blue-eyed parents, have brown eyes.
Also, melanin levels aren’t constant. As we age, they fluctuate. This can make our irises become lighter or darker as we age. To complicate matters more, while your genes might encode for low melanin eyes (blue or green), not every cell of the iris has the same amount of melanin. Iris cells are only slightly different from regular skin cells and we shed them just as fast. This is why under high magnification our irises look pixelated. The same mechanism that makes our skin have dark spots or light spots occurs in our irises.
The more we learn about eye coloration, the more we realize how little we understand genetics. As of now, we know that there are at least 16 different genes that encode for eye color (or more accurately for the amount of melanin in our irises). And they are on multiple chromosomes. And because brown eyes aren’t always dominate, it is very possible that my grey eyed cousin who experiences eye coloration changes, carries a blue eyed gene and a brown eyed gene, just like me. Even though both of her parents have blue eyes. The two different coloration genes allow more fluctuation of the melanin in her irises, just as it does in my hazel eyes. Essentially, the same mechanism with different results, because my genes always encode for more melanin than hers…