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Neutral mutations are changes in DNA sequence that are neither beneficial nor detrimental to the ability of an organism to survive and reproduce. In population genetics, mutations in which natural selection does not affect the spread of the mutation in a species are termed neutral mutations. Neutral mutations that are inheritable and not linked to any genes under selection will either be lost or will replace all other alleles of the gene. This loss or fixation of the gene proceeds based on random sampling known as genetic drift. A neutral mutation that is in linkage disequilibrium with other alleles that are under selection may proceed to loss or fixation via genetic hitchhiking and/or background selection. While many mutations in a genome may decrease an organism’s ability to survive and reproduce, also known as fitness, these mutations are selected against and not passed on to future generations. The most commonly observed mutations detectable as variation in the genetic makeup of organisms and populations appear to have no visible effect on the fitness of individuals and are therefore neutral. The identification and study of neutral mutations has led to the development of the neutral theory of molecular evolution. The neutral theory of molecular evolution is an important and often controversial theory proposing that most molecular variation within and among species is essentially neutral and not acted on by selection. Neutral mutations are also the basis for using molecular clocks to identify such evolutionary events as speciation and adaptive or evolutionary radiations. ==History== Charles Darwin commented on the idea of neutral mutation in his work, hypothesizing that mutations that do not give an advantage or disadvantage may fluctuate or become fixed apart from natural selection. "Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions." While Darwin is widely credited with introducing the idea of natural selection which was the focus of his studies, he also saw the possibility for changes that did not benefit or hurt an organism.〔Darwin, C. (1987; 1859). On the origin of species by means of natural selection : Or the preservation of favoured races in the struggle for life (Special ed.). Birmingham, Ala.: Gryphon Editions.〕 Darwin's view of change being mostly driven by traits that provide advantage was widely accepted until the 1960s. While researching mutations that produce nucleotide substitutions in 1968, Motoo Kimura found that the rate of substitution was so high that if each mutation improved fitness, the gap between the most fit and typical genotype would be implausibly large. However, Kimura explained this rapid rate of mutation by suggesting that the majority of mutations were neutral, i.e. had little or no effect on the fitness of the organism. Kimura developed mathematical models of the behavior of neutral mutations subject to random genetic drift in biological populations. This theory has become known as the neutral theory of molecular evolution. As technology has allowed for better analysis of genomic data, research has continued in this area. While natural selection may encourage adaptation to a changing environment, neutral mutation may push divergence of species due to nearly random genetic drift.〔 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「Neutral mutation」の詳細全文を読む スポンサード リンク
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