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The relationship between race and genetics is relevant to the controversy concerning race classification. In everyday life many societies classify populations into groups based on phenotypical traits and impressions of probable geographic ancestry and socio-economic status - these are the groups we tend to call "races". Because the patterns of variation of human genetic traits are clinal, with a gradual change in trait frequency between population clusters, it is possible to statistically correlate clusters of physical traits with individual geographic ancestry. The frequencies of alleles tend to form clusters where populations live closely together and interact over periods of time. This is due to endogamy within kin groups and lineages or national, cultural or linguistic boundaries. This causes genetic clusters to correlate statistically with population groups when a number of alleles are evaluated. Different clines align around the different centers, resulting in more complex variations than those observed comparing continental groups. For example if a person has light skin, light hair and blue eyes, a combination of traits that seems to have evolved in Northern Europe and is found at a high frequency there, it is probable that person has some recent European ancestry. And by extension, according to the racial categories in use in North America that person is likely to be classified by others, and to self-identify, as "white". In a similar way, Genetic analysis enables us to determine the geographic ancestry of a person pinpointing the migrational history of a person's ancestors with a high degree of accuracy, and by inference the probable racial category into which they will be classified in a given society. In that way there is a distinct statistical correlation between gene frequencies and racial categories. However, because all populations are genetically diverse, and because there is a complex relation between ancestry, genetic makeup and phenotype, and because racial categories are based on subjective evaluations of the traits, it is not the case that there are any specific genes, that can be used to determine a person's race. Research in genetics offers a means to classify humans which is more precise than broad phenotypically based racial categories, given that genetics can provide a much more complex analysis of individual genetic makeup and geographic ancestry, than self identified membership of a racial category. With a blood transfusion, for example, it is vital to know the genetically determined blood type of the donor and recipient, but it is not helpful to know their respective geographic ancestries. Most physical anthropologists consider race to be primarily a social category that does not correspond significantly with biological variation, but some anthropologists, particularly forensic anthropologists, consider race a useful biological category. They argue that it is possible to determine race from physical remains with a reasonable degree of certainty; what is identified is the geographic phenotype. Medical practitioners also sometimes argue that racial categories can be used successfully as proxies to assess risk of those different heritable illnesses that occur with different frequencies among populations of different geographic ancestries. Others argue that this use may be problematic because it risks underestimating risks of individuals from ethno-racial categories that are not considered high-risk, and to overestimate the risk in populations that are, resulting in stigmatization. ==Genetic variation== (詳細はmutations, from migration between populations (gene flow) and from the reshuffling of genes through sexual reproduction. Variation is counteracted by natural selection and by genetic drift; note too the founder effect, when a small number of initial founders establish a population which hence starts with a correspondingly small degree of genetic variation. Epigenetic inheritance involves heritable changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the DNA sequence. Human phenotypes are highly polygenic (dependent on interaction by many genes) and are influenced by environment as well as by genetics. Nucleotide diversity is based on single mutations, single nucleotide polymorphisms (SNPs). The nucleotide diversity between humans is about 0.1 percent (one difference per one thousand nucleotides between two humans chosen at random). This amounts to approximately three million SNPs (since the human genome has about three billion nucleotides). There are an estimated ten million SNPs in the human population. Research has shown that non-SNP (structural) variation accounts for more human genetic variation than single nucleotide diversity. Structural variation includes copy-number variation and results from deletions, inversions, insertions and duplications. It is estimated that approximately 0.4 percent of the genomes of unrelated people differ, apart from copy number. When copy-number variation is included, human-to-human genetic variation is estimated to be at least 0.5 percent. 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「Race and genetics」の詳細全文を読む スポンサード リンク
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