A selfish genetic element drives recurring selective sweeps in the house mouse

A selective sweep is the result of strong positive selection driving newly occurring or standing genetic variants to fixation, and can dramatically alter the pattern and distribution of allelic diversity in a population. Population-level sequencing data have enabled discoveries of selective sweeps associated with genes involved in recent adaptations in many species. In contrast, much debate but little empirical evidence addresses whether “selfish” genes are capable of fixation  thereby leaving signatures identical to classical selective sweeps  despite being neutral or deleterious to organismal fitness. We previously described , a large copy-number variant that causes non-random segregation of mouse Chromosome 2 in females due to meiotic drive. Here we show population-genetic data consistent with a selfish sweep driven by alleles of with high copy number () in natural populations. We replicate this finding in multiple closed breeding populations from six outbred backgrounds segregating for alleles. We find that rapidly increases in frequency, and in most cases becomes fixed in significantly fewer generations than can be explained by genetic drift. is also associated with significantly reduced litter sizes in heterozygous mothers, making it a true selfish allele. Our data provide direct evidence of populations actively undergoing selfish sweeps, and demonstrate that meiotic drive can rapidly alter the genomic landscape in favor of mutations with neutral or even negative effects on overall Darwinian fitness. Further study will reveal the incidence of selfish sweeps, and will elucidate the relative contributions of selfish genes, adaptation and genetic drift to evolution.