HAPLOIDY OR DIPLOIDY - WHICH IS BETTER

ALTHOUGH the evolutionary advantages of sexual reproduction have been extensively discussed 1-3, much less attention has been paid to haploid and diploid phases of the sexual life cycle. The relative lengths of these phases differ greatly in various taxa, including as extremes those with one or the other phase reduced to a single cell. Here we consider the efficiency of elimination of deleterious mutations as an evolutionary force and compare the mutation loads under haploid and diploid selection, L(n) and L2n. With truncation-like selection, partial dominance, and heterozygous effect of a mutation less than about 1/4 its hemizygous effect, L2n < L(n); otherwise L2n > L(n). The difference becomes important when the genomic deleterious mutation rate exceeds about 1 per genome. This suggests that the mutation rate, degree of dominance and mode of selection can be important in life-cycle evolution.