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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 Mutation–selection balance ： ウィキペディア英語版 Mutation–selection balance Mutation–selection balance is an equilibrium in the number of deleterious alleles in a population that occurs when the rate at which deleterious alleles are created by mutation equals the rate at which deleterious alleles are eliminated by selection.〔Herron, JC and S Freeman. 2014. Evolutionary Analysis, 5th Edition. Pearson.〕 The majority of genetic mutations are neutral or deleterious; beneficial mutations are relatively rare. The resulting influx of deleterious mutations into a population over time is counteracted by negative selection, which acts to purge deleterious mutations. Setting aside other factors (e.g. balancing selection and genetic drift), the equilibrium number of deleterious alleles is then determined by a balance between the deleterious mutation rate and the rate at which selection purges those mutations. Mutation–selection balance was originally proposed to explain how genetic variation is maintained in populations, although several other ways for deleterious mutations to persist are now recognized, notably balancing selection. Nevertheless, the concept is still widely used in evolutionary genetics e.g. to explain the persistence of deleterious alleles in actual populations as in the case of spinal muscular atrophy,〔Herron, JC and S Freeman. 2014. Evolutionary Analysis, 5th Edition. Pearson.〕 or, in theoretical models, mutation-selection balance can appear in a variety of ways and has even been applied to beneficial mutations (i.e. balance between selective loss of variation and creation of variation by beneficial mutations).〔http://www.genetics.org/content/176/3/1759.full〕 ==Haploid population== As a simple example of mutation-selection balance, consider a single locus in a haploid population with two possible alleles: a normal allele ''A'' with frequency $p$, and a mutated deleterious allele ''B'' with frequency $q$, which has a small relative fitness disadvantage of $s$. Suppose that deleterious mutations from ''A'' to ''B'' occur at rate $\backslash mu$, and the reverse beneficial mutation from ''B'' to ''A'' occurs rarely enough to be negligible (e.g. because the mutation rate is so low that $q$ is small). Then, each generation selection eliminates deleterious mutants thereby reducing $q$ by an amount $spq$, while mutation creates more deleterious alleles thereby increasing $q$ by an amount $\backslash mu\; p$. Mutation-selection balance occurs when these forces cancel and $q$ is constant from generation to generation, implying $q\; =\; \backslash mu/s$. Thus, provided that the mutant allele is not weakly deleterious (very small $s$) and the mutation rate is not very high, the equilibrium frequency of the deleterious allele will be small. 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「Mutation–selection balance」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.