Hybrid Vigor

The superior performance (growth, fitness) of hybrids has been observed for centuries before the birth of modern genetics. In its simplest case, hybrid vigor may be attributed to the presence of complementary dominant genes. If one parent is AAbb and the other is aaBB, their offspring is AaBb, which has now the favorable dominant alleles at both loci (dominance theory of hybrid vigor). Geneticists measure vigor by reproductive advantage, fitness. The fitness of a homozygous recessive (R) class may be w_aa = 1 − s, where s is the coefficient of selection. The frequency of the homozygous recessives in a population may be determined by the rate of mutation (μ) from allele A to allele a. The average proportion of the recessive class is expected to be: $\hat {\rm p}^2 = {\rm \mu}/{\rm{s}}$ and the average frequency of recessive alleles is expected to be ${\hat{\rm q}} = \sqrt {{\rm \mu /s}}$. The average fitness of the population then becomes \({{\hat {\rm w}}} = {\rm{1}} - {{{\rm s}...