Jakarta, Borneo24.com – Eyes are organs that are very important, so that we as humans can see the world. Uniquely, the human eye has a different color. If you notice, Asian eye color tends to be black or brown.
Meanwhile, Europeans and Americans usually have blue, hazel, or gray eyes. So, why are the eye colors different? To answer it, the mystery of the human body this time discusses the causes of different human eye colors. Reporting from BBC Science Focus, just like skin, eye color is also determined by pigmentation. The iris, which is located behind the cornea or the outermost layer of the eye, consists of several layers.
Its two outermost layers are known as the anterior border, and contain pigment-producing cells called melanocytes. Everyone has the same number of melanocytes, but genetics determines how much pigment or melanin in the iris is produced.
The pigment is the same as the pigment that affects skin color, and the more the production, the darker the color. This means that a person with dark skin will generally have darker, browner eyes. In contrast, fair-skinned people produce less melanin.
Meanwhile, incoming light passes through the anterior border and interacts with the gray cells inside the iris. Then, the light that is reflected back automatically gives the eye a bluer color.
A certain area, called chromosome 15, plays a role in the color of the human eye. This genetic factor causes the difference in the color of our eyes. In that area, there are two genes that are very close together, namely the OCA2 and HERC2 genes.
The P protein, which is produced from the OCA2 gene, is involved in the maturation of melanosomes, which are cellular structures that produce and store melanin. Therefore, this P protein also plays an important role in the amount and quality of melanin present in the iris.
Experts say, if the level of protein P in the iris is less, the melanin in the iris will also be lower. This causes a person’s eyes to turn blue instead of brown. Different eye color caused by melanin not only serves to provide color. Because the melanin in the iris serves as the main protection from ultraviolet rays, so as not to damage the inside of the eye.
Although they don’t play much of a role, several other genes are also said to affect eye color, skin, and even hair. The effect of these genes is likely to combine with the OCA2 and HERC2 genes to produce a range of eye colors in different people.
Researchers say that human eye color can be determined by a single gene, and follows a simple inheritance pattern in which brown eyes are dominant over blue eyes.
So, they believe that if parents have blue eyes, they cannot produce children with brown eyes. Many people also believe that the eyes of a newborn baby will inherit the eyes of their parents and other family members.
However, subsequent research has shown that this model is too simplistic. The research team says that parents with blue eyes can have children with brown eyes, although this is rare. Eye color inherited from parents is more complex, because it involves many genes in the human body. Meanwhile, there are also some disorders that can affect eye color.
For example, ocular albinism is characterized by a severe decrease in the pigmentation of the iris, resulting in very light colored eyes. People with this condition also usually have vision problems.
Another condition called oculocutaneous albinism affects the pigmentation of the skin, hair, and eyes. A person with oculocutaneous albinism tends to have very light-colored irises, fair skin, and white or light-colored hair.
Both ocular and oculocutaneous albinism result from mutations in genes involved in the production and storage of melanin. Next is heterochromia which is characterized by different eye colors in the same individual.
Heterochromia can be caused by genetic changes or problems that arise during eye development. The condition can also be the result of disease or injury to the eye. (***)
–
