Briefly discuss significant features of heterosis and explain the dominance and overdominance hypotheses of heterosis, giving their main features.
Heterosis, or hybrid vigor, refers to the superiority of an F1 hybrid over its parents in terms of growth, yield, fertility, or resistance to stress. Significant features include increased biomass, faster growth rate, higher yield potential, enhanced disease resistance, and improved adaptability.
Two main hypotheses explain heterosis:
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Dominance Hypothesis: Proposed by C. Bruce (1910) and D.F. Jones (1917), it suggests heterosis results from the masking of deleterious recessive alleles by advantageous dominant alleles contributed by both parents. Each parent supplies different favorable dominant genes, leading to a hybrid with a superior combination of traits as harmful recessives are hidden. No single locus necessarily outperforms the homozygous dominant state.
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Overdominance Hypothesis: Suggested by E.M. East (1908) and G.H. Shull (1908), this theory posits that the heterozygous state (e.g., Aa) at a particular locus confers a superior phenotype compared to either homozygous state (AA or aa). This means the combination of two different alleles provides a greater advantage than either allele alone, leading to enhanced vigor.
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