 Thus, studying variation in genomic neighborhoods with relatively low recombination rates, rather than across the whole genome, can yield insights about the relative prevalence of background and hitchhiking selection.Background selection in asexual populations is thought to impact on the speed of Muller's ratchet, the accumulation of irreversible deleterious mutations in nonrecombining populations.Because background selection reduces the effective population size experienced by a region of the genome, and only the portion of an asexual nonrecombining population with the fewest mutations will contribute to future generations, the number of loci where an advantageous mutation could arise and be perpetuated in the population is very small.