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Fig. 6. The effect of genotype combinations (line plots; referred to as physiological epistasis by Cheverud and Routman, 1995) and average genotype effect of gene A across the genetic background (vertical bars; statistical estimation of the average genotype value for the aa and AA genotypes of gene A) for three hypothetical genetic models; (a) a single independent additive gene (gene A); K = 0, (b) a digenic network where gene A interacts with gene B; K = 1, and (c) a trigenic network where gene A interacts with genes B and C; K = 2. K = level of epistasis. Values of the vertical bars show the effect of the two homozygous genotype classes for gene A averaged across all background genotype combinations in the network.
