Will our bundle of joy have blue, green, gray, or brown eyes? Expecting parents love to speculate about the color of their future baby’s eyes. Will he/she have mommy’s dark eyes or daddy’s twinkly blue ones? This question is actually a lot harder to answer than was previously thought. A child’s eye color is not simply determined by a combination of its parents’ or ancestors’ dominant and recessive genes – in fact, a child can have any eye color, despite the color of their parents’ eyes!
What is eye color?
Eye color (or, more precisely, the color of the iris) is determined by the amount of melanin in the back of the iris (the iris pigment epithelium), the melanin content at the front of the iris (in the iris stroma), and the density of the cells of the stroma. There are two types of melanin that determine a person’s eye color: eumelanin and pheomelanin. These pigments also determine skin and hair color. Eumelanin is a brown-black pigment responsible for brown and black hair; pheomelanin is a red pigment and is dominant in red and blond hair.
Genetics of eye color
The genetics of eye color is quite complex and cannot simply be determined on the basis of inheritance alone. It is true that there are two genes (located on chromosome 15) that are predominantly responsible for the difference between blue and brown eyes. The OCA2 gene is 75% responsible for the difference between blue and brown eyes, and the HERC2 gene controls the amount of melanin created by the OCA2 gene. The amount of melanin in the iris combined with light scattering ultimately determines eye color.
The color of your child’s peepers will therefore remain a surprise – even until three years after birth! After all: it takes about three years for eyes to obtain their permanent color (and small changes may occur even after that).
Did you already know these five fascinating facts about eye color?
- There are no green or blue pigments in the human iris or ocular fluid (as explained above, the color is determined by melanin pigments only). Blue and green eyes are the result of the scattering of light in the stroma. Eye color is therefore determined by light, particularly in eyes with low pigmentation levels.
- Sunlight can change the color of the eyes, just like skin. Light eyes turn darker or develop brown spots under the influence of sunlight. In periods when there is less sunlight, such as during winter, eyes regain their normal color.
- Green is the rarest eye color and is most common in the Middle East, Saudi Arabia, Iran, Turkey, Pakistan, and India.
- According to Danish research, blue eyes are probably caused by a gene mutation that arose between 6,000 and 10,000 years ago northeast of the Black Sea. This could mean that all blue-eyed people are descended from the same ancestor.
- Light eyes are more vulnerable to sunlight than dark eyes. Blue, light gray, and green eyes absorb more sunlight through the iris, which stimulates the nerve cells in the back. This is why people with light eyes are more sensitive to bright light than people with darker eyes.