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Thread: Skin color gene study

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    This article comes from a press release by Penn State College of Medicine, so I don't think they will mind if we copy it.
    http://news.psu.edu/story/299166/201...-reveal-shared


    Studies of a skin color gene across global populations reveal shared origins

    All instances of a gene mutation that contributes to light skin color in Europeans came from the same chromosome of one person who most likely lived at least 10,000 years ago, according to Penn State College of Medicine researchers.

    While the genetics of skin color is largely unclear, past research using zebrafish by the College of Medicine’s Keith Cheng identified a key gene that contributes to lighter skin color in Europeans and differs from West Africans. In 2005, Cheng reported that one amino acid difference in the gene SLC24A5 is a key contributor to the skin color difference between Europeans and West Africans.

    “The mutation in SLC24A5 changes just one building block in the protein, and contributes about a third of the visually striking differences in skin tone between peoples of African and European ancestry,” said Cheng, distinguished professor of pathology. Lighter skin color may have provided an advantage due to for the better creation of vitamin D in the lesser sunlight characteristic of northern latitudes.

    In this current part of the project, Victor Canfield, assistant professor of pharmacology, together with Cheng, studied DNA sequence differences across the globe. They studied segments of genetic code that have a mutation and are located closely on the same chromosome and are often inherited together. This specific mutation in SLC24A5, called A111T, is found in virtually everyone of European ancestry.

    A111T is also found in populations in the Middle East and Indian subcontinent, but not in high numbers in Africans. Researchers found that all individuals from the Middle East, North Africa, East Africa and South India who carry the A111T mutation share a common “fingerprint” -- traces of the ancestral genetic code -- in the corresponding chromosomal region, indicating that all existing instances of this mutation originate from the same person.

    These findings were reported in the journal G3.

    The pattern of proportions of people with this lighter skin color mutation indicates that the A111T mutation occurred somewhere between the Middle East and the Indian subcontinent.

    “This means that Middle Easterners and South Indians, which includes most inhabitants of India, Pakistan and Bangladesh, share significant ancestry,” Cheng said.

    This mutated segment of DNA was itself created from a combination of two other mutated segments commonly found in Eastern Asians -- traditionally defined as Chinese, Japanese and Korean.

    “The coincidence of this interesting form of evidence of shared ancestry of East Asians with Europeans, within this tiny chromosomal region, is exciting,” Cheng said. “The combining of segments occurred after the ancestors of East Asians and Europeans split geographically more than 50,000 years ago; the A111T mutation occurred afterward.”

    Cheng plans to next look at more genetic samples to better understand what genes play the most important role in East Asian skin color. He will then use zebrafish to test those suspected genes.

    The differences in skin color affect skin cancer rates. Europeans have 10 to 20 times more instances of melanoma than Africans. However, despite also having lighter skin, East Asians have the same melanoma rates as Africans. The reason for this difference can only be explained after the gene mutations for both groups are found. This understanding could lead to better treatments for melanoma.

    Other scientists on this project were Penn State College of Medicine’s Arthur Berg, Department of Public Health Sciences; Steven Peckins, Steven Wentzel and Khai Ang, Jake Gittlen Cancer Research Foundation and the Division of Experimental Pathology; and Stephen Oppenheimer, Oxford University.
    This thread really belongs in Autosomal.
    Last edited by Jean M; 01-04-2014 at 01:19 PM.

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    The paper is open access: Victor A. Canfield, Arthur Berg, Steven Peckins, Steven M. Wentzel, Khai Chung Ang, Stephen Oppenheimer, Keith C. Cheng, Molecular Phylogeography of a Human Autosomal Skin Color Locus Under Natural Selection, G3 vol. 3 no. 11 2059-2067 (November 1, 2013).

    http://www.g3journal.org/content/3/11/2059.abstract


    World distribution of A111T polymorphism in SLC24A5. The origins of sampled populations are indicated (+). Contours of global frequencies of SLC24A5A111T are shaded according to the frequency/color scale to the right.

    Canfield2013SLC24A5.JPG

    ..the decrease in frequency of A111T to the east of Pakistan suggests that C11 originated farther to the west and after the initial genetic split between western and eastern Eurasians. On this basis, we hold the view that an origin of C11 in the Middle East, broadly defined, is most likely.
    Their conclusion is supported by the data from a recently-published results from ancient DNA. A hunter-gatherer who lived in Central Europe around 6000 BC carried the ancestral form of SLC24A5, rather than the mutation which is almost universal in those of European ancestry today, and which is found in an early farmer in Central Europe who lived around 5000 BC. See I. Lazaridis et al., Ancient human genomes suggest three ancestral populations for Europeans, pre-print online 23 December 2013, Supplementary Information 7.
    Last edited by Jean M; 01-04-2014 at 01:35 PM.

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    Previous work on the same topic was discussed by Razib Khan last year: http://www.anthrogenica.com/showthre...tion&highlight

    Distribution of the two alleles for SLC24A5: black = ancestral; grey = derived.

    slc24a5.jpg
    Last edited by Jean M; 01-04-2014 at 01:01 PM.

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    The hunter gatherers with blue eyes but non-fair skin in Europe must have been a pretty weird looking lot. That is a rare combination today.

    Quote Originally Posted by Jean M View Post
    The paper is open access: Victor A. Canfield, Arthur Berg, Steven Peckins, Steven M. Wentzel, Khai Chung Ang, Stephen Oppenheimer, Keith C. Cheng, Molecular Phylogeography of a Human Autosomal Skin Color Locus Under Natural Selection, G3 vol. 3 no. 11 2059-2067 (November 1, 2013).

    http://www.g3journal.org/content/3/11/2059.abstract


    World distribution of A111T polymorphism in SLC24A5. The origins of sampled populations are indicated (+). Contours of global frequencies of SLC24A5A111T are shaded according to the frequency/color scale to the right.

    Canfield2013SLC24A5.JPG



    Their conclusion is supported by the data from a recently-published results from ancient DNA. A hunter-gatherer who lived in Central Europe around 6000 BC carried the ancestral form of SLC24A5, rather than the mutation which is almost universal in those of European ancestry today, and which is found in an early farmer in Central Europe who lived around 5000 BC. See I. Lazaridis et al., Ancient human genomes suggest three ancestral populations for Europeans, pre-print online 23 December 2013, Supplementary Information 7.

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    Quote Originally Posted by alan View Post
    The hunter gatherers with blue eyes but non-fair skin in Europe must have been a pretty weird looking lot. That is a rare combination today.
    I rather like that combination myself.

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    Probably doesn't exist other than as a minority phenotype among African Americans and South Asians.

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    Quote Originally Posted by newtoboard View Post
    Probably doesn't exist other than as a minority phenotype among African Americans and South Asians.
    I see the combination occasionally in West Indian/British. Leona Lewis is a well-known example, though not as dark-skinned as some such combinations I have seen. https://en.wikipedia.org/wiki/Leona_Lewis

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    Or like some of Frank Frazetta's depictions of Conan.


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    Interesting. On a related note I have wondered what causes light eyes in South Asians to almost exclusively be green or grey. I thought green was darker than blue and grey lighter than blue so that is a weird combination. Maybe because green eyes might be Neolithic and the center of grey eyes is near the Baltic and Black a Seas which might attest to the Eastern European qualities of Asian Steppe nomads.

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