Genetics of eye color

Eye color is mainly determined by genetics. It is one of the genetic traits that depends on the amount and distribution of melanin.

It is true that the genes of both parents contribute to determining the color of an individual's eyes (it is known to be highly heritable), but there are also many other factors that play a role, such as sun exposure or aging.

Melanin and eye color

Melanin is a pigment that colors the skin, eyes and hair. There are two types different melanin:

1. Eumelanin is associated with dark hair, eyes, and skin.
2. The eumelanin is associated with dark hair, eyes and skin.

The color of your eyes depends on the amount, distribution, and type of melanin you have in your iris (the part that colors your eye), which is why babies have light eyes at birth. Their melanin-producing cells are immature and produce little melanin. As the months go by, melanin production increases and they become progressively darker.

Genes associated with eye color

Eye color is an inherited trait influenced by many different genes. Eyes can be green, brown, hazel, gray or blue, mostly. And it has been shown that there are two main factors that determine this trait.

• Amount of melanin in the iris: Melanin is the pigment responsible for brown eyes.
• Expression level of OCA2 and HERC2 genes. OCA2 produces the pigment melanin, while HERC2 limits melanin production by synthesizing proteins that regulate melanin production.

When these genes are expressed at high levels, the individual will have dark brown or black eyes. However, when these genes are not expressed sufficiently, then eyes will be lighter.

To estimate the eye color, in the DNA TEST ADNTRO's work is based on a scientific study that identified genetic variants in genes previously described as genes involved in pigmentation, such as the oculocutaneous albinism II gene (OCA2), tyrosinase-related protein 1 (TYRP1), member 4 (SLC24A4), HERC2 and VASH2. The strongest genetic association is found in the gene HERC2gene associated with pigmentation. The variant which is mainly involved in eye color, reduces the expression of the gene OCA2which translates into a reduced melanin synthesis and, therefore, in obtaining a lighter color.

Exceptions in eye pigmentation

Albinism

Albinism is a genetic disorder that causes an absence of pigment in the body. Albinism can affect both the eyes and the skin. Some forms of albinism cause a complete absence of pigment in the body. Other types cause a partial loss of pigmentation. People with albinism usually have lighter eyes and hair, and sometimes have white patches on the skin. Albinism occurs in all races and ethnic groups.

There are two main types of albinism:

1. Ocular albinism, which affects only the eyes and is caused by mutations in the TYR gene.
2. Ocular albinism, which affects only the eyes and is caused by mutations in the TYR gene.

Heterochromia

Complete heterochromia: Occurs when one eye is each color.

• Complete heterochromiaOccurs when one eye is of each color.
• Sectoral heterochromia: It occurs when the same iris has several colors.
• Central heterochromia: It occurs when the color in the center of the iris is different from the peripheral part, forming a central ring around the pupil of the eye.

This can occur at birth or develop later in life. Heterochromia can range from small differences to large differences in color. These differences are usually caused by genetic factors but can also be caused by trauma to the eye.

Distribution among the different populations

The Caucasian population has the greatest diversity in eye color.

Eye color varies greatly among the different ethnic groups. Dark-skinned people have dark-colored eyes because there is more melanin in their eyes. Fair-skinned people tend to have lighter-colored eyes due to a lack of melanin in the iris although this is not always the case. 

Brown eyes tend to be the most common eyes among people of African, Hispanic, or Asian descent. Blue eyes are the next most common, followed by hazel, gray, green, and amber eyes. Rarely, people even can have pink, gold, or red eyes.