Muller’s ratchet

Muller’s ratchet is the irreversible loss of the least-mutated class in a finite population without recombination, causing harmful mutations to accumulate over generations.

Least-loaded class: The individuals in a population carrying the fewest deleterious mutations. Its random extinction is the key step that advances the ratchet.
Finite population: A population containing a limited number of individuals, subject to random sampling effects. The ratchet depends on finite numbers making rare mutation-free genomes vulnerable to loss.
Obligate asexuality: A reproductive mode in which organisms reproduce without sexual exchange of genetic material. Long-term asexual lineages lack the recombination that could recreate low-mutation genomes.
Muller's ratchet in mitochondria: The accumulation of deleterious mutations in mitochondrial genomes when genetic exchange is limited. Organelle genomes are a prominent setting for ratchet-like mutation accumulation.
Hermann Joseph Muller: An American geneticist who showed that X-rays can induce mutations and studied their evolutionary effects. Muller introduced the ratchet’s underlying argument about mutation accumulation in nonrecombining populations.
Genetic drift: Random changes in allele frequencies caused by finite sampling across generations. Drift can eliminate the least-loaded class even when its members have higher fitness.
Fitness landscape: A representation of how genotype or phenotype maps to reproductive success. The ratchet moves populations among mutation classes with different fitness.
Mitochondrial DNA: The genetic material carried in mitochondria, usually inherited separately from nuclear chromosomes. Its limited recombination makes mutation accumulation relevant to mitochondrial evolution.
Mutational meltdown: A feedback process in which mutation accumulation reduces population size and accelerates further genetic deterioration. Repeated ratchet clicks can help initiate this self-reinforcing decline.
Population genetics: The study of genetic variation within populations and how evolutionary forces change it. The ratchet is a population-genetic explanation of mutation accumulation.

Linked from 6 pages