Eye colour and genetics
Will our bundle of joy have blue, green, gray, or brown eyes? When your parents were expecting you, they loved to speculate about the colour of your eyes. Will you 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 colour is not simply determined by a combination of its parents’ or ancestors’ dominant and recessive genes – in fact, a child can have any eye colour, despite the colour of their parents’ eyes!
What is eye colour?
Eye colour (or, more precisely, the colour of the iris) is determined by the amount of pigment (called melanin) in the iris. There are two types of melanin that will determine your eye colour: eumelanin and pheomelanin. These pigments also determine skin and hair colour. 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.
In Iris her irisses the pigment heomelanin is dominant.
Genetics of eye colour
The genetics of eye colour is quite complex and cannot simply be determined on the basis of inheritance alone. It is true that there are two genes 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 colour.
The colour of a 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 colour (and small changes may occur even after that).
Did you already know these five fascinating facts about eye colour?
- There are no green or blue pigments in the human iris or ocular fluid (as explained above, the colour is determined by melanin pigments only). Blue and green eyes are the result of the scattering of light in the front of the iris. Eye colour is therefore determined by light, particularly in eyes with low pigmentation levels.
- Sunlight can change the colour 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 colour.
- Green is the rarest eye colour 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.