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Melanin, Skin Color, and Genetics

written by: Nirvanagrewal•edited by: Paul Arnold•updated: 9/11/2009

Time to go under the skin, to look at skin color and the genetic basis of skin pigmentation.

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    Melanin: Pigment for Skin Color

    Friends The pigment that gives color to your skin is melanin. It is also responsible for the color of your eyes. Melanin protects our skin from harmful ultraviolet radiation of the sun by absorbing the rays.

    More melanin pigment is produced by people with dark skin as compared to light skinned persons. There are two types of melanin pigment. Pheomelanin is red in color and eumelanin is very dark brown in color. The quantity and type of melanin are determined by a handful of genes. We inherit one copy of each of these genes from each of our parents and each gene comes in several different versions known as alleles. It's this that's responsible for the sheer variety of skin tones.

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    Variation in genes and skin color

    One gene responsible for the production of melanin pigment is SLC24A5. It is found that there are two variations of SLC24A5:

    1) One variation is with the amino acid called threonine, which is responsible for the light color of the skin.

    2) Second variation is associated with the amino acid alanine, which is responsible for the dark color of the skin.

    Some of the other genes that affect the function of the melanin pigment include ASIP, MC1R, TYR, KITL, HERC2 and OCA. The most important protein responsible for variation in skin color is MC1R.

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    Zebra fish and skin pigmentation

    Scientists have found up to 100 genes responsible for variation in the skin color. And research conducted on zebra fish is shedding some light on Zebrafish the mystery of our own skin color. Humans and fish have similar pigment cells, containing pigment granules called melanosomes. Differences in the number, size and nature of these determine the many different shades of skin color. For example, Europeans have fewer, smaller and lighter melanosomes than those from people of West Africa.

    In 2005 scientists from Pennsylvania State University College of Medicine in Hershey, Pa., found that the zebra fish variant called "golden" also had fewer, smaller and less heavily pigmented melanosomes than normal zebra fish. The dark stripes on these fish are caused by melanin, the same pigment in humans. The golden variety is lighter than normal zebra fish and the scientists found that this was due to a single mutation on SLC24A5. When the scientists introduced the human version of the gene into the golden zebra fish they observed that the dark stripes appeared, and the fish were no longer golden.

    So what does this have to do with human skin color? In humans 93% of Africans, Native Americans, and East Asians had the original version of the gene, but most European-American people (about 98%) had the version with the single genetic mutation.

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    References:

    Blake, E. 2000. Why Skin Comes in Colors. http://www.calacademy.org/calwild/winter2000/html/horizons.html

    Alaluf S, Atkins D, Barrett K, Blount M, Carter N, et al. The impact of epidermal melanin on objective measurements of human skin colour. Pigment Cell Res. 2002b;15:119–126.

    www.prlog.org/10167358-zebrafish-journal-publishes-skin-pigmentation-studies-that-shed-light-on-the-evolution-of-race.html

    Pictures:

    http://www.flickr.com/photos/iloveblue/2528773058/

    http://www.flickr.com/photos/ciamabue/3472958822/