The accumulation of deleterious mutations that can lead to the extinction of a population of asexual organisms. H. J. Muller pointed out in 1964 that in asexual species mutations tend to accumulate because of the random loss of individuals with the least mutated genomes. In the absence of back mutation, the process is irreversible. Once mutants replace healthy genes, the good ones never come back and so the process resembles a ratchet wheel, which moves in only one direction. Muller proposed that sexuality arose because it allowed crossing over to occur between homologous chromosomes from parents carrying different mutants. Recombinant offspring with mutant-free genomes could thus arise and halt the action of the rachet. The term Muller ratchet was coined by J. Felsenstein in 1974.
Subjects: Ecology and Conservation — Genetics and Genomics.