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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 fixation index ： ウィキペディア英語版 fixation index The fixation index (FST) is a measure of population differentiation due to genetic structure. It is frequently estimated from genetic polymorphism data, such as single-nucleotide polymorphisms (SNP) or microsatellites. Developed as a special case of Wright's F-statistics, it is one of the most commonly used statistics in population genetics. ==Definition== Two of the most commonly used definitions for FST at a given locus are based on the variance of allele frequencies between populations, and on the probability of Identity by descent. If $\backslash bar$ is the average frequency of an allele in the total population, $\backslash sigma^2\_S$ is the variance in the frequency of the allele between different subpopulations, weighted by the sizes of the subpopulations, and $\backslash sigma^2\_T$ is the variance of the allelic state in the total population, FST is defined as : $F\_\; =\; \backslash frac\; =\; \backslash frac)\}$ Wright's definition illustrates that FST measures the amount of genetic variance that can be explained by population structure. This can also be thought of as the fraction of total diversity that is not a consequence of the average diversity within subpopulations, where diversity is measured by the probability that two randomly selected alleles are different, namely $2p(1-p)$. If the allele frequency in the $i$th population is $p\_i$ and the relative size of the $i$th population is $c\_i$, then : $F\_\; =\; \backslash frac)-\backslash sum\; c\_i\; p\_i(1-p\_i)\})\}\; =\; \backslash frac)-\; \backslash overline\})\}$ Alternatively, : $F\_\; =\; \backslash frac\}$ where $f\_0$ is the probability of identity by descent of two individuals given that the two individuals are in the same subpopulation, and $\backslash bar$ is the probability that two individuals from the total population are identical by descent. Using this definition, FST can be interpreted as measuring how much closer two individuals from the same subpopulation are, compared to the total population. If the mutation rate is small, this interpretation can be made more explicit by linking the probability of identity by descent to coalescent times: Let T0 and T denote the average time to coalescence for individuals from the same subpopulation and the total population, respectively. Then, : $F\_\; \backslash approx\; 1-\backslash frac$ This formulation has the advantage that the expected time to coalescence can easily be estimated from genetic data, which led to the development of various estimators for FST. 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「fixation index」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.