Genetic basis of heterosis. Deleterious recessive genes avoidance hypothesis. Scenario A. Fewer genes are under-expressed in the homozygous individual. As well, gene expression in the offspring is equal to the expression of the best parent. Overdominance hypothesis. Scenario B. Over-expression of certain genes in the homozygous. (The size of the circle depicts the expression level of gene A)

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Genetic basis of heterosis. Deleterious recessive genes avoidance hypothesis. Scenario A. Fewer genes are under-expressed in the homozygous individual. As well, gene expression in the offspring is equal to the expression of the best parent. Overdominance hypothesis. Scenario B. Over-expression of certain genes in the homozygous. (The size of the circle depicts the expression level of gene A)