"The effect of selfing on the mutation load near a site under balancing selection"Stetsenko, RomanBalancing selection is a type of selection maintaining polymorphism among genetic variants and is caused by diverse biological mechanisms. Because it generates an increase in the frequency of heterozygotes, segregating deleterious mutations in closely linked regions can accumulate as they are masked by selection if they are partially recessive, creating a “sheltered load”. Previous theoretical work found that a sheltered load can be maintained in tightly–linked sites with those under balancing selection, mainly focusing on self-incompatibility or mating-type loci in outcrossing species. Empirical evidence for a sheltered load was found in genetic regions that are linked to the self-incompatibility locus in several Angiosperms, and evidence for an accumulation of putatively deleterious variants was found linked to the MHC in humans. Numerous genome regions displaying signatures of balancing selection have been described in self-fertilising species, despite very high selfing rates (such as in Caernorhabditis elegans). However, it is not yet clear how the mating system affects the prevalence of sheltered loads and whether these can cause significant fitness effects in self-fertilising species. Using an analytical model, we study the deterministic and the stochastic trajectories of deleterious mutations that are completely or partially linked to a balancing site under arbitrary selfing rates. The approximations obtained are checked against forward-in-time simulations using SLiM. We discuss the implications of the results regarding the mutation load in selfing species, and for detecting it using genome data. |
« back