Either parental imprinting or non-symmetry of parental mating type
frequencies with respect to maternal and paternal genotypes may
result in 
being different from 
.
First, consider a single diallelic DS locus with random mating and
Hardy-Weinberg equilibrium, and assume that 
and
. Then, for ASPs,
and hence, by equation (1), 
.
Consider now a strict-recessive model with general mating type
frequencies and 
.
