Genetic analysis of environmental variation

Abstract

Summary: Environmental variation (V_E) in a quantitative trait – variation in phenotype that cannot be explained by genetic variation or identifiable genetic differences – can be regarded as being under some degree of genetic control. Such variation may be either between repeated expressions of the same trait within individuals (e.g. for bilateral traits), in the phenotype of different individuals, where variation within families may differ, or in both components. We consider alternative models for defining the distribution of phenotypes to include a component due to heterogeneity ofV_E. We review evidence for the presence of genetic variation inV_Eand estimates of its magnitude. Typically the heritability ofV_Eis under 10%, but its genetic coefficient of variation is typically 20% or more. We consider experimental designs appropriate for estimating genetic variance inV_Eand review alternative methods of estimation. We consider the effects of stabilizing and directional selection onV_Eand review both the forces that might be maintaining levels ofV_Eand heritability found in populations. We also evaluate the opportunities for reducingV_Ein breeding programmes. Although empirical and theoretical studies have increased our understanding of genetic control of environmental variance, many issues remain unresolved.