Advantage To Mutators
Consider a hypothetical mutator allele that increases the mutation rate in the area around it.
--M------A--
On this chromosome the gene M is a mutator allele, increasing the rate of mutation in the surrounding area. A is an allele which is fixed in the population. Due to the increased mutation rate, the A allele may be mutated into a new, advantageous allele, A*.
--M------A*--
The individual in which this chromosome lies will now have a selective advantage over other individuals of this species, so the allele A* will spread through the population by the normal processes of natural selection. M, due to its proximity to A*, will also increase in frequency. This hitchhiking only works when M is very close to the beneficial allele that it has created by mutation. A greater distance would increase the chance of recombination separating M from A*, leaving M alone with any deleterious mutations it may have caused. For this reason, hitchhiking on beneficial mutations is most likely to affect the evolution of mutation rates in asexual species where recombination cannot disrupt linkage.
Read more about this topic: Genetic Hitchhiking
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