GENETICS OF EYE COLOUR 

Edited by, SNEHA MAVIS

The amount of melanin contained in the front layers of the iris, the structure surrounding the pupil, determines a person's eye color. Melanin is produced by specialized cells called melanosomes. Although everyone has roughly the same number of melanocytes, the amount of melanin in melanosomes and the number of melanosomes within melanocytes differ.

In people with blue eyes, a small number of melanosomes contain a small amount of melanin. Green eyes have a moderate quantity of melanin and a moderate number of melanosomes, but brown eyes have a large amount of melanin stored within the large number of melanosomes.

GENES INVOLVED IN DEVELOPMENT OF EYE COLOUR:

The amount of melanin stored is determined by genes involved in the production, transport, and storage of melanin. To date, scientists have discovered more than 150 genes that determine eye color.

One region of chromosome-15 contains two genes that play important roles in determining eye color. One gene, OCA2, codes for a protein called P Protein, which is involved in melanosome maturation and influences the amount and quality of melanin stored in the iris. A number of genetic changes (polymorphisms) in this gene limit the amount of P protein produced, resulting in a lighter eye color.

HERC2 is the name of the major gene involved. Intron 86 on this gene regulates OCA2 expression, activation and deactivating it as needed. At least one polymorphism in this intron decreases OCA2 expression and function, reducing the amount of P protein generated.

Pattern of eye colour inheritance: 

The pairing of genes passed down from each parent determines a child's eye color, which is thought to entail at least three gene pairs. EYCL1 (also known as the gey gene) and EYCL3 (also known as bey2 gene) and the two key gene pairs that geneticists have focused on.

Alleles are the many variations of genes. The gey gene has one allele that causes green eyes and one allele that causes blue eyes. There are 2 alleles of the bey2 gene: one for brown eyes and one for blue eyes. The allele for brown eyes is always dominant over the other 2 alleles, and the allele for green eye is always dominant over the allele for blue eyes, which is always recessive. This means that even if both parents have the same eye color, their child can have a different eye colour.