why do we have different colored eyes

The instance of a person having two differently colored eyes is pretty uncommon, just 11 out of every 1,000 Americans. This uncanny trait is caused by several factors, and can actually develop over time. Iris color develops during the first few months after birth, with the levels of the pigment melanin determining how dark eyes will become. The less melanin expressed in the iris, the lighter a person's eyes look, and vice versa. Sometimes, though, the concentration and distribution of melanin isn't uniform, which leads to a condition known as heterochromia. This condition can present itself in different ways. There's complete heterochromia, when
is a distinctly different color, say, one blue and one brown. Central heterochromia is when the eyes show various colors, such as a blue iris with a golden-brown ring around the pupil. And sectoral heterochromia is when one iris has a splash of color that's different from its overall hue, a trait that actress Kate Bosworth has. Eye pigmentation abnormalities are not necessarily a sign of an underlying health condition.


This is known as simple heterochromia, and is generally inherited from a parent. Heterochromia, however, is a common feature of several inherited genetic disorders. For example, Waardenburg syndrome causes children to experience hearing loss, and varying degrees of heterochromia. Another inherited disorder that lists heterochromia as a symptom is neurofibromatosis, which affects the nervous system and causes tumors to form on nerve tissue. Tumor formation inside the eye can cause heterochromia. Irregular iris coloring can also be caused by an injury to the eye, such as a punch leading to bleeding within the eye. An infection or mild inflammation that affects only one eye can cause it, as can the presence of a foreign object in the eye, because that can lead to. Heterochromia can also be caused by glaucoma, which is a group of eye conditions that damage the nerve that carries visual information from the eye to the brain. The sudden onset of heterochromia could be the sign of an underlying medical condition, and a complete eye exam should be conducted by an ophthalmologist to rule out any serious causes.


Got a question? and we'll look for an expert who can crack it. 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 Kollam, Kerala.

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