Fig. 1. An example of genotypic reaction norms illustrating the concept of phenotypic plasticity. In the simple case of two environments, the lines represent the norms of reaction of each genotype, while the slope is a measure of the degree and pattern (positive or negative) of phenotypic plasticity. So, for example, genotypes 1 and 3 are both plastic, but display opposite patterns in response to the same environments; genotype 2, on the other hand, shows little plasticity for this trait in this environmental set.