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Distance from Africa, not climate, explains within-population phenotypic diversity
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[QUOTE]Originally posted by The Explorer: [QB] ^Interesting additions. From a DNA phylogenetic standpoint, as heterozygosity increases, linkage disequilibrium tends to decrease; and vice versa, as heterozygosity decreases in a dataset, chances are the same dataset will be marked by greater linkage disequilibrium. African samples generally tend to sport more heterozygosity; the authors in the following, for example, saw this as well: [b][i]Global Haplotype Diversity in the Human Insulin Gene Region[/i][/b] [i]John D.H. Stead1,3,4, Matthew E. Hurles2 and Alec J. Jeffreys1 [/i] [i]The insulin minisatellite (INS VNTR) has been intensively analyzed due to its associations with diseases including diabetes. We have previously used patterns of variant repeat distribution in the minisatellite to demonstrate that genetic diversity is unusually great in Africans compared to non-Africans. Here we analyzed variation at 56 single nucleotide polymorphisms (SNPs) flanking the minisatellite in individuals from six populations, and we [b]show that over 40% of the total genetic variance near the minisatellite is due to differences between Africans and non-Africans[/b], far higher than seen in most genomic regions and [b]consistent with differential selection acting on the insulin gene region[/b], most likely in the non-African ancestral population. [b]Linkage disequilibrium was lower[/b] in African populations, with evidence of clustering of historical recombination events. Analysis of haplotypes from the relatively nonrecombining region around the minisatellite revealed a star-shaped phylogeny with lineages radiating from an ancestral African-specific haplotype. [b]These haplotypes confirmed that minisatellite lineages defined by variant repeat distributions are [i]monophyletic[/i] in origin.[/b] These analyses provide a framework for a cladistic approach to future disease association studies of the insulin region within both African and non-African populations, and they identify SNPs which can be rapidly analyzed as surrogate markers for minisatellite lineage. The insulin minisatellite, located within the promoter of the human insulin gene, has been intensely investigated for nearly two decades due to its associations with diseases such as diabetes (Bell et al. 1984; Bennett and Todd 1996). Most studies have analyzed populations of European descent where [b]low diversity at the minisatellite[/b] combined with [b]strong linkage disequilibria[/b] in flanking regions make it difficult to distinguish between etiological and associated variants (Bennett and Todd 1996; Doria et al. 1996). The identification of etiological polymorphisms in the insulin region may therefore require analysis of a range of different populations, in particular those [b]showing a greater range of haplotype diversity than that seen in Europeans...[/b][/i] http://www.egyptsearch.com/forums/ultimatebb.cgi?ubb=get_topic;f=8;t=003824;p=1#000000 [/QB][/QUOTE]
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