Genetic correlation

Genetic correlation is the correlation between the genetic values of two traits, arising when both are influenced by the same genes or linked genes. It is the quantitative-genetic expression of pleiotropy: where pleiotropy describes the qualitative fact that one gene affects multiple traits, genetic correlation measures the directional and statistical strength of this shared genetic influence. Genetic correlations constrain evolution by rotating the response to selection away from the direction of selection pressure, making populations evolve along genetically accessible trajectories rather than fitness-optimal ones. The genetic correlation matrix is to evolutionary dynamics what the inertia tensor is to mechanical systems: it defines the directions in which change is easy and the directions in which it is resisted.