Fig. 1. Sex in ants, bees, and wasps is determined at a single gene. When females mate with males that share a sex allele in common (allele a in our example), half of their diploid progeny, which were intended to be daughters, will be homozygous at sex gene (i.e. have two copies of the allele, eg. AA, or BB, or CC, etc.), and will develop into diploid males. Normal females are heterozygous at the sex gene (i.e. have two different sex alleles, eg. AB, BC, AC, etc.), while normal haploid males have a single sex allele. Since females only fertilize their eggs to produce daughters, DMP is best viewed as increased female mortality. In some species, diploid males have low viability. More often however, diploid males are effectively sterile: They are viable, achieve matings, but do not father diploid daughters, which reduces the reproductive success of their mates.