On average, they do not differ from the original population. Therefore, the mean variance of the heterozygotes is completely lost in their offspring. Thus the dominance effect which caused the phenotypic variance in the heterozygotes is not heritable. The variance of a character is divided into genetic and environmental effects. Understand how variance is calculated.
Relatives have similar genotypes, producing the correlation between relatives.
Correlation among relatives is one way to calculate V A , additive genetic variance. Correlation of environments is a confounding consideration, whenever genetic correlation is being studied. Heritability is the proportion of phenotypic variance that is additive. This relation is true only if the environments of parents and offspring are not correlated. Again, correlation of environments is a confounding consideration, whenever genetic correlation is being studied.