An elucidation of over a century old enigma in genetics-Heterosis

Abstract

Recognition and exploitation of hybrid vigor or heterosis among individual crosses of plants and animals has a long and distinguished history. Its manifestation is influenced by a combination of genetic, epigenetic, phenotypic, and environmental factors. Although heterosis is known to be governed by both dominant and epistatic gene action, its expression is greatly influenced by nonlinear interaction among epigenetic and phenotypic (phenomic) components. The magnitude of heterosis is generally inferred post hoc by the phenotypic performance of hybrids among laboriously made individual crosses. The expression of dominance, however, is nonlinear at the cellular level and obeys the principles underlying metabolic flux. Then, is it possible to exploit these relationships to predict heterosis? Vasseur and colleagues have indeed demonstrated the feasibility of such an approach in a series of experiments taking integrated biochemical and computational approaches, as well as testing these results on large samples of model organisms. The results offer promise toward phenomic prediction of heterosis across a wide array of organisms.

Fig 1. Phenotypic expression of dominance in different genotypes, their fitness and enzyme flux.

(A) Major classes of phenotypic diversity and their fitness in interindividual crosses of homozygote recessive (aa; P2, worst parent) and dominant (AA; P1, best parent) genotypes. With monogenic inheritance, phenotypic expression of heterozygotes (Aa) could deviate from (1) MP approaching dominants (best parent) and (2) inferior or superior (Tps) to both recessive and dominant genotypes (worst and best parents, respectively). (B) Wright’s view of the phenotypic manifestation of dominance of genotypes as a function of enzyme flux. Note the flux of heterozygotes exceeds midparent values (modified from [26]). MP, midparent; Tp, transgressive phenotype.