We review the contributions of epistasis to the genetic variation expected in segregating populations, utilising models with arbitrary specified genotypic values or non-linear relationship between observed phenotype and underlying additive genotype. Even with substantial epistasis, rather small amounts of epistatic variance are generated. With multiple loci, the proportion of epistatic variance does not increase because the interactions also contribute to main effects and hence the additive variance. Utilisation of additive x additive variance with an appropriate relationship matrix is unlikely to be effective because the contributions are small and are not retained over generations. Incorporation of genomic data has more promise if focussed on tightly linked regions, but this will be successful only if such regions contribute substantially to the variance, and such evidence is lacking. At this stage we think selection efforts will be, and should be, focussed on the additive component.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Genetic Improvement Programs: Breeding objectives, economics of selection schemes, and advances in selection theory, , 019, 2014
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