mutatorallelen

Mutatorallelen are genetic variants that increase the overall mutation rate of an organism by reducing the fidelity of DNA replication or repair. They arise when genes involved in DNA maintenance acquire mutations that weaken their function. In bacteria, mutator alleles are often loss-of-function changes in elements of the DNA mismatch repair system, which normally corrects replication errors before they become mutations.

Mutatorallelen can affect different pathways, including mismatch repair, proofreading during replication, base excision repair, or nucleotide excision repair. The result is a higher rate of mutations across the genome, with the mutational spectrum reflecting the pathway impaired. Consequently, some lineages accumulate mutations at substantially higher rates than typical strains.

From an evolutionary perspective, mutatorallelen can be advantageous when the environment changes rapidly, by increasing the supply of beneficial mutations and speeding adaptation. However, they carry a genetic load from deleterious mutations and are often selected only transiently or in conjunction with other adaptive changes. In many microbial populations, mutator alleles can spread by hitchhiking with advantageous variants, even if they reduce average fitness in stable conditions.

Mutator phenotypes are observed across diverse organisms, most prominently in bacteria but also in yeast and in cancer cells, where deficiencies in DNA repair (such as mismatch repair) produce elevated mutation rates that can fuel evolutionary dynamics within tumors. Thus mutatorallelen reflect a trade-off between generating genetic diversity and accumulating harmful changes, influencing genome evolution and adaptation.