Why do different people have different coloured eyes like blue, black, or brown?, asks Akriti Singh from Jabalpur, Madhya Pradesh.
Eye colour eyes is determined by the amount of melanin in the iris, density of proteins, and the frequency of the scattering of light by the turbid medium in the stroma of the iris. The colour of the iris is determined by the amount of melanin pigments, the way the melanin is distributed in the eye and the ratio of eumelanin to pheomelanin. Eye colours have been divided into nine categories and as many as 16 genes have been associated with eye colour inheritance. The main genes associated with eye colour include OCA2 and HERC2 and both are located in Chromosome 15. The HERPC2 gene generally regulates OCA2 expression and a specific mutation within HERC2 gene is partly responsible for blue eyes. Different single-nucleotide polymorphism within OCA2 are associated with blue and green eyes.
Brown eyed genes are dominant and blue eyed genes tend to be recessive. In humans brown eyes are predominant eye color worldwide whereas blue eyes have become increasingly rare . Blue eyed people share one common ancestor and it is believed that the mutation that caused blue eyes happened between 6,000-10,000 years ago. Grey eyes are darker than blue eyes and have less melanin pigments. Grey eyes is determined by the amount of melanin pigments in the iris and density of proteins. Only 2 per cent of the world has green eyes and have moderate or low amounts of melanin. Hazel eyes have colour midway between the lightest blue and the darkest brown eyes and have large amount of melanin in the anterior border of the iris. According to some scientists eye colour can change dramatically in the first few years of life, as many babies are born with blue eyes , later develop green or brown eyes.
Dr. Sainudeen Pattazhy
Environmentalist and Chief Editor
Journal of Scientific Research & Reviews
Kollam, Kerala.
