Our DNA contains a collection of instructions or genes that cells utilise to carry out daily functions and interact with their surroundings. Traditionally, the genetics of eye colour was thought to be dependent on a single gene, with brown eyes predominating over blue eyes. But now, scientists have revealed that many genes affect the genetics of eye colour. The genes regulate the quantity of melanin in the iris’ specialised cells.
In this article, we’ll look at the science of pigmentation and the genetics of eye colour.
Introduction to pigments and their role in the genetics of eye colour
The amount of melanin (along with the type of melanin) determines the colour of human eyes, skin, and hair. Melanin is created by specialised cells known as melanocytes. They store melanin in intracellular compartments known as melanosomes. The total number of melanocytes in each person is generally the same, but the amount of melanin inside each melanosome and the count of melanosomes within a melanocyte can vary. As a result, the genetics of eye colour is not as simplistic as initially proposed.
A variety of genes are involved in the generation, processing, and transportation of melanin. Scientists have identified approximately 150 distinct genes that control the genetics of eye colour in humans. A number of these genes have been identified as a result of research into genetic abnormalities in humans. Others were revealed as a result of comparative genomic investigations of mouse coat colour and fish pigmentation patterns.
How do the genetics of eye colour work?
The amount of light reflected off the iris determines the eye colour in humans. The degree of melanin pigment in the iris determines eye colour from the spectrum of blue to hazel to brown. Blue eyes have a tiny number of melanosomes that carry very little pigment. Green–hazel eyes have moderate pigment levels and melanosome quantity. Brown eyes have high melanin levels stored throughout numerous melanosomes.
The OCA2 gene, found on chromosome 15, appears to be important in modulating the brown/blue colour spectrum. P-protein, which OCA2 produces, is involved in the synthesis and processing of melanin. Individuals with OCA2 mutations that impede P-protein production are born with albinism. These people have light-coloured hair, eyes, and complexion. Brown eyes are associated with the genotype that results in high levels of P-protein. At first glance, this seems to be the dominant/recessive model of the genetics of eye colour taught in biology schools for decades.
However, while genetic differences in and around this gene can explain around three-fourths of eye colour variance, OCA2 is not the factor involved in the genetics of eye colour. According to a recent study that matched eye colour to OCA2 status, a variety of additional genes (including TYRP1, ASIP, and ALC42A5) participate in the melanin pathway and influence eye colour. These genes’ combined efforts may increase melanin levels, resulting in hazel or brown eyes, or decrease total melanin, resulting in blue eyes.
This explains how two blue-eyed parents can have green- or brown-eyed children (an impossible condition according to the Davenport single gene hypothesis). The combination of colour alleles obtained by the child might result in a more significant amount of melanin than either parent possessed separately.
The eyes are one of the most complicated and sensitive organs of our body. Scientists are still actively working on uncovering the secrets of our eyes. In such a scenario, you should make sure that you entrust only experts like Centre For Sight with any problems related to your eyes. Centre For Sight has the largest eye care network in the country, with over 1500 skilled doctors and cutting-edge equipment. We can solve any eye condition with our medical skill and compassionate treatment. To receive the best possible care for your eyes, contact us today or visit our website!
Article: The genetics of eye colour explained!
Author: CFS Editorial Team | May 10 2021 | UPDATED 02:30 IST
*The views expressed here are solely those of the author in his private capacity and do not in any way represent the views of Centre for Sight.