Mutational load and the advantage of sex

Summary The mutational load for dominant deleterious mutations is 2u in sexual populations (where u is the mutation rate), but this reduces to between 2u and u when the selective disadvantage of the heterozygote is less than about 0·03. In contrast, it is shown here that in the case of asexual population, the situation is different and the mutational load remains at 2u even when the mutations are only very mildly deleterious in the heterozygote. As such mutations could be very common, sexually reproducing organisms may have a substantially smaller mutational load than asexual groups.