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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク F-statistics ： ウィキペディア英語版 F-statistics In population genetics, ''F''-statistics (also known as fixation indices) describe the statistically expected level of heterozygosity in a population; more specifically the expected degree of (usually) a reduction in heterozygosity when compared to Hardy–Weinberg expectation. ''F''-statistics can also be thought of as a measure of the correlation between genes drawn at different levels of a (hierarchically) subdivided population. This correlation is influenced by several evolutionary processes, such as mutation, migration, inbreeding, natural selection, or the Wahlund effect, but it was originally designed to measure the amount of allelic fixation owing to genetic drift. The concept of ''F''-statistics was developed during the 1920s by the American geneticist Sewall Wright, who was interested in inbreeding in cattle. However, because complete dominance causes the phenotypes of homozygote dominants and heterozygotes to be the same, it was not until the advent of molecular genetics from the 1960s onwards that heterozygosity in populations could be measured. ''F'' can be used to define effective population size. == Definitions and equations == The measures FIS, FST, and FIT are related to the amounts of heterozygosity at various levels of population structure. Together, they are called ''F''-statistics, and are derived from ''F'', the inbreeding coefficient. In a simple two-allele system with inbreeding, the genotypic frequencies are: :$p^2(1-F)\; +\; pF\backslash text\backslash mathbf;\backslash \; 2pq(1-F)\backslash text\backslash mathbf;\backslash textq^2(1-F)\; +\; qF\backslash text\backslash mathbf.$ The value for F is found by solving the equation for F using heterozygotes in the above inbred population. This becomes one minus the observed number of heterozygotes in a population divided by its expected number of heterozygotes at Hardy–Weinberg equilibrium: :$F\; =\; 1-\; \backslash frac))\}\; ))\}\; =\; 1-\; \backslash frac)\}\; ))\},\; \backslash !$ where the expected value at Hardy–Weinberg equilibrium is given by :$\backslash operatorname(f(\backslash mathbf))\; =\; 2pq,\; \backslash !$ where ''p'' and ''q'' are the allele frequencies of A and a, respectively. It is also the probability that at any locus, two alleles from a random individuum of the population are identical by descent. For example, consider the data from E.B. Ford (1971) on a single population of the scarlet tiger moth: From this, the allele frequencies can be calculated, and the expectation of ''ƒ''(AA) derived: : $p\; =\; (Aa)\; \backslash over\; 2\; \backslash times\; (\backslash mathrm(AA)\; +\; \backslash mathrm(Aa)\; +\; \backslash mathrm(aa))\}\; =\; 0.954$ : $q\; =\; 1\; -\; p\; =\; 0.046\backslash ,$ : $F\; =\; 1-\; \backslash frac\; =\; 1-\; =\; 0.023$ The different ''F''-statistics look at different levels of population structure. FIT is the inbreeding coefficient of an individual (I) relative to the total (T) population, as above; FIS is the inbreeding coefficient of an individual (I) relative to the subpopulation (S), using the above for subpopulations and averaging them; and FST is the effect of subpopulations (S) compared to the total population (T), and is calculated by solving the equation: :$(1-F\_)(1-F\_)\; =\; 1-F\_,\; \backslash ,$ as shown in the next section. 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「F-statistics」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.