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[QUOTE]Originally posted by MindoverMatter718: [QB] [QUOTE]Originally posted by Chimu: [qb] Got similar response. [QUOTE]----- Original Message ----- From: Heather Norton Sent: Thursday, January 14, 2010 7:20 PM Subject: Re: Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians Dear Jaime, In the 2006 paper we said that in [b]the San the light allele at a particular SNP in the OCA2 gene (rs1800404) was most often found in the derived state--that is, most individuals carried one or two "A" alleles as opposed to the "G" allele which predominated in the other African populations surveyed. We determine whether a SNP is ancestral or derived based on which allele is found in other primate species--usually chimpanzee. In this case chimpanzees, orangutans, and macaques all carry the G allele at this site[/b]--the A allele has not been observed (to my knowledge) in these species. [b]However, remember that pigmentation is controlled by multiple loci, and although we know that OCA2 plays an important role in skin pigmentation, I would be very surprised to learn that the derived allele at this particular SNP can explain all of the variation in pigmentation between the San and other, more darkly pigmented African populations.[/b] So, while the San carry a derived allele at rs1800404, [b]it's possible that at other SNPs they carry an allele common in other primates with light skin underneath their fur. At those loci (should they ever be identified), the San would be considered to carry the ancestral allele, while other, more darkly pigmented populations would carry the derived allele[/b] (which would presumably cause a greater amount of eumelanin to be produced). It's [u]entirely possible[/u] that the San's pigmentation can be explained by a mix of derived alelles (like the one at rs1800404) and ancestral alleles shared with other primates but not with their neighboring populations. Remember, we are talking about one mutation in OCA2--there are many, many other mutations in this gene that could (and do) affect pigmentation (most notably eye pigmentation). So, I would say that this particular mutation (rs1800404) plays *some* role in the lighter pigmentation of the San, but that there are probably other mutations (either in OCA2 or in other genes) that contribute to the phenotype as well. [b]I actually don't know if the # of differences between chimp and San at OCA2 is greater than the # of differences between chimp and other African populations--it would be interesting to find out[/b] (it would also be interesting to find this out for other pigmentation genes as well). The mutations that we believe are responsible for lighter pigmentation in European and East Asian populations are derived both relative to chimpanzees as well as to what is observed in most African populations (sometimes, when the chimpanzee sequence is not available we assume that the allele most common in African populations is the ancestral allele). Also, we know that at least some of those mutations (like rs1426654 in SLC24A5) alter the protein that is produced--another sign that they play an important role in influencing phenotype. Best, ~Heather[/QUOTE]So the San carry one mutation in the OCA2 that is not in chimpanzees that other Africans have (And chimpanzees are light skinned). But Dr. Tishkoff doesn't know, overall which populations have the most mutations on the OCA2 gene, and which ones are closer to the ancestral one shared with chimpanzees. The derived genes specified in the OOA populations are known because they are different to African populations. Again, she is basically saying she doesn't know which skin tone is the derived state because other parts in the OCA2 play a role, and other genes play a role. So still inconclusive. And any claims of derivation of the San (in ONE mutation on the OCA2, does not fully explain the lighter skin of the San, nor the lighter skin of the Bisa Sandawe in equatorial Tanzania. [IMG]http://i46.tinypic.com/2ihmpom.jpg[/IMG] [IMG]http://i45.tinypic.com/2you1d0.jpg[/IMG] [IMG]http://i45.tinypic.com/35iss5i.jpg[/IMG] [IMG]http://i49.tinypic.com/2d6wnd3.jpg[/IMG] [/qb][/QUOTE]Lol chimu, its not inconclusive as Norton specifically notes that the San do carry the derived allele A, and not ancestral G on the OCA2 allele. G which is shared by non human primates so its ancestral and dominate in other neighboring populations. This was the whole point whether or not the San carried this derived allele at high frequencies and as shown they really do. Sorry chimu but you're done with. [/QB][/QUOTE]
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