Wednesday, 21 March 2012

Mystery of Human eye colour

Mystery of Human eye colour

The complex genetics of human eye colour

We all have different eye colours ranging from brown to blue, and many researches have shown this is one of the physical traits in the human body that is genetically determined. Variation in the colour of our eyes depends on the amount of melanin in the iris. “Melanin” is a skin pigment that determines the skin, hair and eye colour, and in turn it is produced by the pigment-producing cells called “melanocytes”, which are located in the outer surface epidermis, and in the middle and inner layers of the eye (White & Rabago-Smith 2011). So, basically dark-eyed people have more melanin than those people having blue or green-eyes.

For the last few decades, geneticists have thought that eye colour is decided based on dominant (brown) and recessive (blue) genes according to Mendelism, and those genes exist on chromosome 15 and 19 (GlassesCrafter 2011). However current genetic research has shown that eye colour determination is a far more complex process than we have thought and involves a number of genes. For example, a recent study conducted by a team of scientists in the University of Queensland discovered the fact that small variations on a gene called OCA2, which controls the amount of melanin pigment produced, are responsible for a significant portion of the total variation in people’s eye colour, approximately 74% (BBC 2006).  Strum (2008) suggested that DNA sequence variations called "single nucleotide polymorphisms" regulate protein production in the OCA2 gene, which is the key point to explaining about reducing melanin in the body of blue-eyed people.

A common ancestor
Recently, Danish researchers fascinated by the genetics of eye colour made an interesting announcement that people who have blue eyes have a common ancestor who originated about 10,000 years ago. Based on the research conducted with 150 members of a Danish family and a number of people who were born in Turkey and Jordan, Professor Eiberg(2008) claimed that every subject had the same genetic mutation occurring in the OCA2 gene, and this resulted in limited melanin production, consequently “turned off the ability to produce brown eyes." This gave him a clue that originally every person had brown eyes, however, since one individual experienced genetic mutation, the blue-eyed trait transferred from generation to generation, therefore blue-eyed people have the same ancestor in terms of evolution.
Consequently, studying the genetics of human eye colour is such a fascinating area for geneticists, and it is still an ongoing process to explain how exactly the eye colour is determined. Presumably, continuous effort in studying genetic variations would contribute to a cure for genetic disorders, like albinism, in the future.
References list
BBC 2006, Genetics of eye colour unlocked, BBC, viewed 14 March 2012,         
Eiberg, Hans 2008, ‘How one ancestor helped turn our brown eyes blue’, The independent, viewed 10, March 2012,                                                                                                     
GlassesCrafter 2012, Why Are My Eyes Blue? The Genetics of Eye Color, GlassesCrafter, viewed 12 March 2012,                                                                                                                  
Strum, R 2008, ‘Can blue-eyed parents produce brown-eyed children?’, bioscience-explained, vol. 4, NO. 1, viewed 11 March 2012,                                                                                     
White, D & Rabago-Smith, M 2011, ‘Genotype–phenotype associations and human eye color’, Journal of Human Genetics, vol. 56, no. 5, viewed 13 March 2012,                                            

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