Relative importance of the epistatic components of genotypic variance in non-inbred populations

There are theoretical approaches about genic interaction in polygenic systems and methodologies to confirm its occurrence. However, some relevant aspects as the relative importance of the epistatic components of genotypic variance deserve further investigation. Considering complementary, duplicate, recessive, dominant, dominant and recessive epistasis, duplicate genes with cumulative effects and non-epistatic genic interaction, relative magnitudes of the epistatic components of genotypic variance assuming digenic epistasis were analyzed. Regardless of the type of epistasis and gene frequencies, the magnitudes of the epistatic components are proportional to the complexity of the polygenic system, the number of interacting genes and the magnitude of the epistatic effects relative to the deviations a (difference between the genotypic value of the homozygote with greater expression and the mean of the genotypic values of the homozygotes) and d (due to dominance). Only in simple genetic systems or in those where complementary, recessive, dominant and recessive, duplicate genes with cumulative effects, or non-epistatic gene interaction types of epistasis predominate, with high frequencies of dominant genes, epistatic components can be of reduced or negligible magnitude.