Genetic variance
Genetic variance is a concept outlined by the English biologist and statistician Ronald Fisher in his Fisher's fundamental theorem of natural selection which he outlined in his 1930 book The Genetical Theory of Natural Selection which postulates that the rate of change of biological fitness can be calculated by the genetic variance of the fitness itself. Fisher tried to give a statistical formula about how the change of fitness in a population can be attributed to changes in the allele frequency. In his 1997 paper Lessard pointed out that Fisher had made no restrictive assumptions in his formula concerning fitness parameters, mate choices or the number of alleles and loci involved.
Phenotypic variance, usually combines the genotype variance with the environmental variance. Genetic variance has three major components: the additive genetic variance, dominance variance, and epistatic variance.
Additive genetic variance involves the inheritance of a particular allele from your parent and this allele's independent effect on the specific phenotype, which will cause the phenotype deviation from the mean phenotype. Dominance genetic variance refers to the phenotype deviation caused by the interactions between alternative alleles that control one trait at one specific locus. Epistatic variance involves an interaction between different alleles in different loci.
Heritability refers to how much of the phenotypic variance is due to variance in genetic factors. Usually after we know the total amount of genetic variance that is responsible for a trait, we can calculate the trait heritability. Heritability can be used as an important predictor to evaluate if a population can respond to artificial or natural selection.
Broad-sense heritability, H2 = VG/VP, Involves the proportion of phenotypic variation due to the effects of dominance and epistasis variance. Narrow-sense heritability, h2 = VA/VP, refers to the proportion of phenotypic variation that is due to additive genetic values (VA).
...
Wikipedia