Gene and genotypic frequencies for a deleterious mutant in mutation selection balance are derived for an infinite population undergoing partial self-fertilization. These provide formulations of mean survival and the mutational load. Obtained also are the average number of mutant genes and affected individuals stemming from a single mutant.
As a concomitant effect on frequencies at a neutral locus the mutational load is distributed disproportionately among the neutral genotypes. For partially recessive mutant genes on the 1, 1-sh, 1-s scale, the effect is to increase the frequency of the heterozygote and to decrease the frequencies of homozygotes at the neutral locus relative to the frequencies expected with complete neutrality. This apparent overdominance at the neutral locus has been shown to be connected with identity disequilibrium rather than linkage disequilibrium. It increases generally as s and h decrease, and as the proportion of self-fertilization and the degree of linkage increase. The apparent overdominance with complete linkage is generally less than double that for free recombination. For partially dominant mutant genes, h ≥ ½, the effects on the frequencies of heterozygote and homozygotes at the neutral locus are reversed.