Muller's Ratchet

∞ generated and posted on 2016.12.16 ∞

Manifestation of genetic drift where, in small, non-sexual populations, there will be a tendency for the wild-type genotype to be lost.

With Muller's Ratchet those with the best genes can die off, never to return, if populations are both too small and members can't swap genes among themselves.

Muller's ratchet does not represent a loss of specific alleles, just a loss of genotypes from populations. The problem is that in the absence of sex and/or horizontal gene transfer, the only way to recover a given genotype, once lost, is through mutation, such as back mutation, which is assumed to rare.

Instead of "wild type", one can substitute the phrases "least mutated" or "most fit" to describe that genotype (or genotypes) that is lost to Muller's ratchet.

Figure legend: Schematic representation of Muller's Ratchet. Note loss of wild-type genotype from the population due to genetic drift but failure to lose, at least proximately, any wild-type alleles from the same population (here A, B, and C). Recovery of the wild-type genotype is possible only via reverse mutation (low likelihood) or genetic recombination in association with sex (also low likelihood given predominantly clonal populations).

Avoidance of Muller's ratchet is cited as one advantage to participating in sex, though it is a problem that requires some means of addressing only given small population sizes as associated with genetic bottlenecking or instead founder effects.

There actually is a song called "Muller's Ratchet", by a band called The Rakes.