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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 Linkage disequilibrium ： ウィキペディア英語版 Linkage disequilibrium In population genetics, linkage disequilibrium is the non-random association of alleles at different loci i.e. the presence of statistical associations between alleles at different loci that are different from what would be expected if alleles were independently, randomly sampled based on their individual allele frequencies. If there is no linkage disequilibrium between alleles at different loci they are said to be in linkage equilibrium. Linkage disequilibrium is influenced by many factors, including selection, the rate of recombination, the rate of mutation, genetic drift, the system of mating, population structure, and genetic linkage. As a result, the pattern of linkage disequilibrium in a genome is a powerful signal of the population genetic forces that are structuring it. In spite of its name, linkage disequilibrium may exist between alleles at different loci without any genetic linkage between them and independently of whether or not allele frequencies are in equilibrium (not changing with time).〔 Furthermore, linkage disequilibrium is sometimes referred to as gametic phase disequilibrium; however, the concept also applies to asexual organisms and therefore does not depend on the presence of gametes. ==Formal Definition== Suppose that among the gametes that are formed in a sexually reproducing population, allele ''A'' occurs with frequency $p\_A$ at one locus (i.e. $p\_A$ is the proportion of gametes with ''A'' at the first locus), while at a different locus allele ''B'' occurs with frequency $p\_B$. Similarly, let $p\_$ be the frequency of ''A'' and ''B'' occurring together in the same gamete (i.e. $p\_$ is the frequency of the ''AB'' haplotype). The association between the alleles ''A'' and ''B'' can be regarded as completely random when the probability of ''A'' and ''B'' occurring together in a randomly selected gamete $p\_$ is just the probability that ''A'' and ''B'' independently occur in the same gamete, which is given by $p\_\; p\_$. If $p\_$ differs from $p\_\; p\_$ for any reason, then there is non-random association between ''A'' and ''B'' and we say that there is linkage disequilibrium between these alleles. The level of linkage disequilibrium between ''A'' and ''B'' can be quantified by the coefficient of linkage disequilibrium $D\_$, which is defined as - p_p_. |} Linkage disequilibrium corresponds to $D\_\; \backslash neq\; 0$. In the case $D\_=0$ we have $p\_\; =\; p\_\; p\_$ and the alleles ''A'' and ''B'' are said to be in linkage equilibrium. The subscript ''AB'' on $D\_$ emphasizes that it is a property of the alleles ''A'' and ''B''. Different alleles at the same loci may have different coefficients of linkage disequilibrium. Linkage disequilibrium can be defined in a similar way for asexual populations using population allele frequencies. Furthermore, it is also possible to define linkage disequilibrium between three or more alleles, however these higher order associations are not commonly used in practice.〔 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「Linkage disequilibrium」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.