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[QUOTE]Originally posted by MindoverMatter718: [QB] [QUOTE]Originally posted by Chimu: [qb] [QUOTE]From: Heather Norton To: Jaime Andres Pretell Sent: Friday, February 27, 2009 4:29 PM Subject: Re: Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians Dear Mr. Pretell, Thanks for your interest in my work. Yes, these genes "exist" in other primates. That is to say, primates have stretches of DNA sequence that produce the same protein in humans and in chimps, and these are usually found in the same corresponding region on their chromosomes. So, it would be correct to say that both humans and chimps, for example, have the gene for ASIP, OCA2, MC1R, etc. When we look at the sequence of individual nucleotides (A, C, G, or T) that make up a particular gene, we may see small differences between chimps and humans. So, for example, at one place in the OCA2 gene chimps might all have a "G" base, where humans all carry an "A" in the corresponding position. This is what is known as a fixed difference, and studying fixed differences may help us to understand why humans and chimps differ for certain traits. However, you can imagine that there may be other cases were chimps carry a "G" at a certain position while some humans carry the "G" and others carry an "A". When we see the same nucleotide being carried in both species (in this case, the "G") we call it the ancestral allele. When the nucleotide differs (in this case, the "A") we refer to it as the derived allele. The term allele here is used to refer to a different versions of the same gene. So, while chimps and humans have the same pigmentation genes (so do mice, and pigs, and fish), they may carry slightly different versions of that gene. Sometimes we see slightly different versions of a gene within the same species. These different versions may explain some of the physical differences (like skin pigmentation) that we see among individuals. In other cases, though, these differences don't affect the protein that the gene produces, and so they don't seem to explain physical differences. The question of the San and Sandawe is an interesting one. [b]We are not sure if the alleles that explain why their pigmentation is so different from neighboring populations reflect new (derived) mutations or if instead maybe they are actually ancestral alleles shared with light-skinned primates.[/b] I would say that this is an area of open investigation. As for ASIP and OCA2...I think that even if you ignored the contribution of these two genes to pigmentation variation we would still see good range of diversity. For example, genes like SLC24A5 and MATP also have a major impact on phenotype. I would also assume that in the past there was variation in human skin color. It would be unlikely to be as much variation as we see across the human species today, since today modern humans live in a range of environments where different pigmentation types are more or less adaptive. In general, I would say that the pigmentation of early humans, who originated in Africa, was dark to provide protection against the damage that ultraviolet radiation can do. However, when we look at populations in Africa today (or populations living in other places where ultraviolet radiation is strong) we see a wide range of variation in pigmentation--I suspect that if we could go back in time we would probably see similar levels of diversity to those that we see in Africa today. Thanks again for your interest--if you have any more questions, please let me know. Cheers, ~Heather [/QUOTE]Again. Bisa Sandawe lighter than Bantu, and no evidence that it is the derived gene. Norton clearly says that while, like Jabonski, she beleives that the environment will favor darker skin, the genetic allow for the full diversity from the get go, and history has shown us that lighter (as in San and Bisa Sandawe lighter) populations have existed from South Africa all the way to Tanzania. Area for open investigation. [/qb][/QUOTE]Wonder how long you've been waiting for this response.. :rolleyes: lol. In any event, it is clear from Norton's paper she was citing Jablonski on the derived alleles, correct? So why didn't you e-mail Jablonski? As it is pretty clear there are derived alleles that Norton was referencing from Jablonski, correct? Get back to your email box, and get Jablonski's response on the derived alleles that she notes to be high in the San hunter gatherers of south Africa, then we might give you a chance. Also, regardless of which way you split it, Norton made clear to you that..... [i]In general, I would say that the pigmentation of early humans, who originated in Africa, was [b]dark[/b] to provide protection against the damage that ultraviolet radiation can do. --Norton[/i] [/QB][/QUOTE]
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