eyes colour

What does eye color depend on?

The basic color of the eyes should be blue because the light rays, when they hit the eye, are spread in an inversely proportional way to their wavelength. Given that the radiations in the blue range, by virtue of their low wavelength, possess a high diffusibility, the eye has as its base color all the shades of blue.

At the level of the iris, variable amounts of melanin can be present, the same pigment responsible for the color of the skin. Depending on the amount of melanin produced, the eye takes on a rather wide range of shades, ranging from blue to black. If the amount of melanin is low or zero, the eyes are blue, while in the opposite case the iris takes on a brown color. When there is a different amount of melanin in the iris of the two eyes, the case of heterochromia can occur.

Why do all babies have blue eyes?

In the first months of life at the level of the iris the production of melanin is inhibited. In fact, the pigmentation process takes a few months to fully activate (it becomes noticeable around the sixth-seventh month of life). The extent to which the ocular melanocytes begin to produce melanin is dependent on the genetic heritage of the child and determines the coloring of the eyes. In dark-skinned children (black and latin race), for example, this phenomenon does not exist and the color of the eyes, already dark at the time of birth, does not change with growth.

The blue color of the eyes is recessive, while brown is dominant. This means that the child will have blue eyes as an adult only when the gene for this feature is present on both homologous chromosomes. In other words, two parents with brown eyes have very little chance of giving birth to a child with blue eyes (see figure), although in the first months of life this occurrence is quite common.

In the figure the concept is simplified for educational purposes, in reality the color of the eyes is determined by different genes, which account for the different shades present in nature (bluish, gray-green, green, light brown, black, etc.).

CONTINUE: Alterations in skin color "