|
Genetic history of indigenous peoples of the Americas primarily focus on Human Y-chromosome DNA haplogroups and Human mitochondrial DNA haplogroups.〔((Detailed hierarchical chart) )〕 Autosomal "atDNA" markers are also used, but differ from mtDNA or Y-DNA in that they overlap significantly.〔 The genetic pattern indicates Indigenous Amerindians experienced two very distinctive genetic episodes; first with the initial peopling of the Americas, and secondly with European colonization of the Americas.〔 The former is the determinant factor for the number of gene lineages, zygosity mutations and founding haplotypes present in today's Indigenous Amerindian populations. Analyses of genetics among Native American and Siberian populations have been used to argue for early isolation of founding populations on Beringia and for later, more rapid migration from Siberia through Beringia into the New World. The microsatellite diversity and distributions of the Y lineage specific to South America indicates that certain Amerindian populations have been isolated since the initial colonization of the region.〔Am J Hum Genet. 2003 September; (Y-Chromosome Evidence for Differing Ancient Demographic Histories in the Americas ) 73(3): 524–539.- Published 2003 July 28.PMCID: PMC1180678〕 The Na-Dené, Inuit and Indigenous Alaskan populations exhibit Haplogroup Q-M242; however, they are distinct from other indigenous Amerindians with various mtDNA and atDNA mutations.〔〔 This suggests that the peoples who first settled the northern extremes of North America and Greenland derived from later migrant populations than those who penetrated further south in the Americas. Linguists and biologists have reached a similar conclusion based on analysis of Amerindian language groups and ABO blood group system distributions. ==Background== The Y chromosome is passed down directly from father to son; all male humans (Y chromosomes) today trace back to a single prehistoric father termed "Y-chromosomal Adam" originating in Africa. The Y chromosome spans about 60 million base pairs (the building blocks of DNA) and represents about 2 percent of the total DNA in all human cells. The original "Y chromosomal Adam"-DNA sequencing has mutated rarely over the 20,000 generations, but each time a new mutation occurs, there is a new branch in a haplogroup, resulting in a new subclade (single-nucleotide polymorphism (SNP)). Both females and males inherit their Mitochondrial DNA (mtDNA) only from their mother. MtDNA mutations are also passed down relatively unchanged from generation to generation, so all humans share the same mtDNA-types. The logical extension of this is that all humans ultimately trace back to one woman, who is commonly referred to as Mitochondrial Eve. This line of biological inheritance, therefore, stops with each male.〔 Consequently, Y-DNA is more commonly used by the general public for tracing genetic heritage of a direct male line. An autosome (atDNA) is a chromosome that is not a sex chromosome – that is to say, there are an equal number of copies of the chromosome in males and females. Autosomal DNA testing is generally used to determine the "genetic percentages" of a person's ancestry from particular continents/regions or to identify the countries and "tribes" of origin on an overall basis. Genetic admixture tests arrive at these percentages by examining locations (SNPs) on the DNA where one nucleotide has "mutated" or "switched" to a different nucleotide.〔 One way to examine the support for particular colonization routes within the American landmass is to determine if a closer relationship between zygosity and geography is observed when "effective" geographic distances are computed along these routes, rather than along shortest-distance paths. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Genetic history of indigenous peoples of the Americas」の詳細全文を読む スポンサード リンク
|
