Phenotypic, Genetic and Environmental Correlations

Abstract

Estimates of phenotypic and genetic correlations are widespread throughout the literature of animal breeding. In many instances the estimate of a phenotypic correlation between two traits exceeds that of the corresponding genetic correlation, a result which may seem unexpected at first sight because phenotype includes genotype and one might anticipate the correlation between phenotypes to be larger than that between genotypes. This paper investigates the relationship between these two correlations, involving the heritabilities of the two traits and the correlation between the environmental (including error) effects which form part of the phenotypic expressions of the traits. The relationship is used to discuss the conditions under which (i) the genetic correlation will exceed the phenotypic correlation and (ii) the environmental correlation will be negative. An example is given and illustrated graphically.