Wednesday, 4 April 2012


Blue Eyes & the Genetic Link to a Common Ancestor


Society has always been intrigued by the diverse range in human physical characteristics. Recent studies into the links between eye colour and genetics have discovered a link between blue eyes and a mutation which occurred some 6-10000 years ago. The study undertaken by Hans Eiberg, a Danish geneticist, has claimed to have drawn the connection between all people who have blue eyes and a linking common ancestor.

In order to understand this advance in the field of genetics one must understand the gene which controls the pigmentation of one’s eye, skin and hair colour. The gene OCA2, is responsible for the transportation of tyrosine, a substrate used in melanin production. Melanin is the pigment which gives colour to eyes, skin and hair. It is the concentration and distribution of melanin within ones iris which determines its colour. (Branicki et al., 2007)

Previously OCA2 has been associated to albinism, a condition where no melanin is produced resulting in pale skin, hair and red irises(Sulem et al., 2007) Blue eyes result from a mutation which has occurred in the HERC2 gene, adjacent to OCA2, essentially ‘switching-off’ brown eye production. This happens due to the limited production of melanin. This ‘switch’does not however “turn-off”the gene as that would result in albinism and not blue eyes. Eiberg has said that originally all humans had brown eyes but this mutation has resulted in blue colouration. (Eiberg etal.,2008)

A study at the University of Copenhagen tested a series of individuals from Turkey, Denmark and Jordan. It was vital to select people from a range of ethnicities and locations in order to determine that the results would not be specific to one group of people. The results showed that 97% of people with blue eyes had the same mutation on the same chromosome. It was concluded that if blue eye mutation had been a random occurrence the area of the mutation would differ in each individual, rather than on the same place in the significant majority. This has prompted researchers to draw the link between people with blue eyes and a common ancestor They have concluded this by observing that the DNA for people with brown and green eyes greatly varies in each individual, whilst the DNA of people with blue colouration displays considerably lesser variation. From this observation the conclusion that all blue-eyed people must have a common link to an ancestor who first possessed this unique mutation was drawn. (Eiberg et al., 2008)

Whilst this discovery is no doubt intriguing, it does not go as far as to tell us why such a mutation would have occurred. There are no known advantages or disadvantages to eye colouration, and thus this discovery does not provide society with the possible answers to its purpose. However,this advance in genetics research should satisfy many individual’s curiosity about the variations in human appearances.


Link to the original article:
http://www.sciencedaily.com/releases/2008/01/080130170343.htm

by Natalia Tejs

References

·         Branicki, W., Szczerbińska, A., Brudnik, U., Wolańska-Nowak, P., & Kupiec, T. (2008). The OCA2 gene as a marker for eye colour prediction. Forensic Science International: Genetics Supplement Series, 1(1), 536-537. doi: 10.1016/j.fsigss.2007.10.062. Retrieved from http://www.sciencedirect.com.ezproxy.library.uq.edu.au/science/article/pii/S1875176808000930

·         Eiberg, H., Troelsen, J., Nielsen, M., Mikkelsen, A., Mengel-From, J., Kjaer, K., & Hansen, L. (2008). Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression. Human Genetics, 123(2), 177-187. doi: 10.1007/s00439-007-0460-x. Retrieved from http://www.springerlink.com/content/2045q6234h66p744/fulltext.html

·         Sulem, P., Gudbjartsson, D.F., Stacey, S.N., Helgason, A., Rafnar, T., Magnusson, K.P., Manolescu, A., Karason, A., Palsson, A., Thorleifsson, G., Jakobsdottir, M., Steinberg, S., Pálsson, S., Jonasson, F., Sigurgeirsson, B., Thorisdottir, K., Ragnarsson, R., Benediktsdottir, K.R., Aben, K.K., Kiemeney, L.A., Olafsson, J.H., Gulcher, J., Kong, A., Thorsteinsdottir, U. & Stefansson, K. (2007). Genetic determinants of hair, eye and skin pigmentation in Europeans. Nature genetics, 39(12), 1443-52. Retrieved from http://search.proquest.com.ezproxy.library.uq.edu.au/docview/222631969/fulltextPDF?accountid=14723

Chosen Article:
·         University of Copenhagen (2008, January 30). Blue-eyed Humans Have A Single, Common Ancestor. ScienceDaily. Retrieved from http://www.sciencedaily.com/releases/2008/01/080130170343.htm

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