...
Post A Reply
my profile
|
directory
login
|
register
|
search
|
faq
|
forum home
»
EgyptSearch Forums
»
Deshret
»
Challenge to Chimu
» Post A Reply
Post A Reply
Login Name:
Password:
Message Icon:
Message:
HTML is not enabled.
UBB Code™ is enabled.
[QUOTE]Originally posted by Chimu: [QB] [QUOTE]Originally posted by The Explorer: Take note: Elsewhere I wrote, with regards to the dichotomy in trends seen between "Original" Inland Melanesians and "CEPH" Island Melanesians: Further extensions of variations detected amongst Melanesians can be explained by successive demographic events [i]After[/i] their African ancestors migrated over 40ky ago. The “original Melanesian sample” appears to have more ancestral pigmentation genes in common with tropical Africans, which is to be expected given that they are direct descendants of the earliest Eurasians, as demonstrated as follows with the [b]OCA2[/b] gene…[/QUOTE] [QUOTE]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.[/QUOTE] [QUOTE]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.[/QUOTE] [QUOTE][i]In general, the [b]derived[/b] allele (associated with lighter pigmentation) is [b]most common in Europeans and East Asians[/b], and the [b]ancestral[/b] allele [b]predominates in sub-Saharan Africa and Island Melanesia[/b].[/i][/QUOTE]Nice strawman. The derived gene in Europeans and Asians, is not the gene responsible for lightness in the Bisa Sandawe. [QUOTE]Three loci, TYR A192C, MATP C374G, SLC24A5 A111G, show very strong signals of European-specific divergence. At all 3 loci, Europeans have the highest frequency of the derived alleles relative to the other 5 populations.[/QUOTE]The San so called derived gene is [QUOTE]At OCA2 355, the derived allele (linked with lighter pigmentation) occurs at its highest frequencies across Europe and Asia but is also relatively common among Native American populations (18–34%) and is present at much lower frequencies (0–10%) among Bantu-speaking African groups. In contrast, the ancestral allele associated with dark pigmentation has a shared high frequency in sub-Saharan African and Island Melanesians. A notable exception is the relatively lightly pigmented San population of Southern Africa where the derived allele predominates (93%), although this may be simply due to small sample size (n = 14).[/QUOTE]Note that there is an ASSUMPTION that it is derived because of the lack of frequency in Melanesians and Africans, but there is NO EXPLANATION as to why the San's allele would be derived. In other words, a hypothesis. And when pressed, Dr. Norton stated succinctly, that they didn't know for sure. [QUOTE]The mutations in the OCA2 gene may well have implications on imparting paleness, as demonstrated in the south African San people… [i]The lightly pigmented hunter-gatherer San populations of Southern Africa is exceptional in having a high frequency of the [b]derived allele[/b] relative to geographically proximate and more darkly pigmented African populations (Jablonski and Chaplin 2000), further [b]supporting the importance of OCA2 in regulating normal variation in pigmentation[/b]. The widespread distribution of the derived allele in the CEPH-Diversity Panel suggests that [b]it is not necessarily a new mutation, nor has it been restricted to a specific geographic area[/b].[/i][/QUOTE] [QUOTE]The question of the San and Sandawe is an interesting one. 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. I would say that this is an area of open investigation.[/QUOTE] [QUOTE]While it seems plausible that the “derived” OCA2 gene came to being before the out-of-Africa migration that give rise to modern Eurasians, it doesn’t appear that this derived allele was necessarily widespread, and may well have been later on selected for in European and East Asians… [i]Interestingly, [b]derived allele frequencies[/b] at this locus are [b]quite different between Native American (15%) and East Asian populations (45%)[/b], suggesting that perhaps the [b]derived allele at this locus did not reach very high frequencies[/b] in East Asians until [b]after the colonization of the Americas[/b][/i] The pattern observed between the "original" Island Melanesians and the sub-Saharan populations, and that between the "original" Island Melanesians and the "CEPH" Island Melanesians, suggests that OAC2 variations different from those of the former pair, must be derive variants. The shared markers between sub-Saharan African and the "original" Island Melanesians would otherwise have to be explained off by "convergent evolution" at possibly different points in time; what are the odds of that happening at a single locus? However, as suggested above, while the other OAC2 variant-- different from those shared between said sub-Saharans and the "original" Island Melanesian samples--may well be the "derived" variant, it doesn't appear to have emerged [i]after[/i] the oft talked about successful OOA migrations of a.m.hs. Thus it could have simply contributed to natural African variation, and then was carried off in [i]modest[/i] frequencies with OOA migrants, whereupon it would later be selected for in certain groups [explaining the relatively high frequencies therein], as mentioned above. So, again, it is hard to determine the ages of the mutations themselves, but from distribution patterns, extrapolations thereof of the molecular chronology of the markers is possible. [/QUOTE]Again, dealing with derived genes in Asians, not the supposed derived gene in Sandawe. [QUOTE]Originally posted by Bob_01: Do you have any paper regarding melanin level suggesting that? Just because someone (whoever they are) may observe that doesn't mean it's true. [/QUOTE]1947-Trevor-The Physical Characters of the Sandawe [QUOTE]Originally posted by Bob_01: [qb] According to Jablonski and Chaplin 2000's study, Sandewe has similar reflectance levels as Namibians or those from Zaire. The San populations found in Botswana and South Africa are much lighter. That excerpted posted by Mind suggesting that San has a high level of derived alleles also include San populations with higher reflectance levels. [URL=http://www.yanaiweb.com/genome/HumanVariation/Jablonski_JHE_2000.pdf]www.yanaiweb.com/genome/HumanVariation/Jablonski_JHE_2000.pdf[/URL] [/qb][/QUOTE]That would be the Tehla Sandawe. The Sandawe have been mixing extensively with Bantu populations. [QUOTE]From: "Imogene Lim" To: "Jaime Pretell" Sent: Tuesday, July 29, 2008 7:17 PM Subject: RE: Rock-shelter Use Today: An Indicator of Usandawe Prehistory If you look at recent photographs, there has been increasing intermarriage between groups. Certainly when I conducted my field work some 20 years ago, there were those who shared strong resemblance to their southern counterparts, the Ju/'hoansi and other Bushmen/San, the only other true Khoisan language speakers. After being in the field over a year, I was "darker" in skin tone than many of the Sandawe in the community where I lived. Eric Ten Raa who studied among the Sandawe in the early 1960s has photographs in one particular article showing the distinction between the Tehla and Bisa Sandawe. The latter are the ones who exhibit the classic Sandawe phenotype. Regards, Imogene[/QUOTE] [QUOTE]Originally posted by The Explorer: I just gave you an [i]actual[/i] *genetic explanation*, the one actually [i]published[/i] and conducted by a group of geneticists, and not a [i]personal correspondence[/i] with one participant, as to why the most parsimonious explanation of OAC2 variant--implicated in Sans and later in Europeans and East Asians--is one wherein it could only have been a [i]derived[/i] allele, as opposed to the upstream one. This explanation is *supported* by the study, as cited! [/QUOTE]Nice try. Not supported by the study. A statement of fact was made, but no actual evidence was provided. And Dr. Norton clarified that they really did not know. [QUOTE]Originally posted by The Explorer: Here's an even [i]easier[/i] challenge than addressing my [i]earlier[/i] post above, which is apparently too difficult for Chimu: Give us this "ancestral OCA2" marker shared between primates and humans! [/QUOTE]Humans are primates. And irrelevant question. you have yet to show anything other than conclusive statements that the OCA2 in San is derivative. [/QB][/QUOTE]
Instant Graemlins
Instant UBB Code™
What is UBB Code™?
Options
Disable Graemlins in this post.
*** Click here to review this topic. ***
Contact Us
|
EgyptSearch!
(c) 2015 EgyptSearch.com
Powered by UBB.classic™ 6.7.3