In evolutionary genetics, Muller's ratchet (named after Hermann Joseph Muller, by analogy with a ratchet mechanism) is the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner.
Muller proposed this mechanism as a theory to explain the evolution of sex. Although Muller's ratchet is proposed to explain the success of sexual reproduction over asexual reproduction, the negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms which, while they reproduce asexually, also undergo other forms of recombination. This effect has also been observed in those regions of the genomes of sexual organisms which do not undergo recombination.
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