The ability of an individual to change the phenotype in response to changes in the environment is called phenotypic plasticity or environmental sensitivity . Plasticity has a genetic basis can be observed at the biochemical, physiological, behavioural, and other levels of the organism. Plasticity is often described by reaction norms, which describe the phenotypic expression of a genotype as a function of the environment Differences in plasticity between individuals (genotypes) will result in genotype by environment interaction (GxE) , i.e. the difference between the expected phenotypic values of two genotypes is not the same in two environments. If the difference changes sign, we have reranking of genotypes.