The analysis of quantitative variation in natural populations with isofemale strains

Abstract

Isofemale strains are having an increasing role in the analysis of variability of ecological and behavioural traits in natural populations. This paper therefore considers the association between heritability and phenotypic variation within and between isofemale strains. Heritability from an isofemale strain analysis approximates narrow heritability over a wide range of dominance values, particularly when genes contributing to variation in a trait are at intermediate frequencies. Meaningful heritability estimates require that isofemale strains are maintained at a population size greater than 50 and tested within 5 generations after establishment. Values of heritabilities for morphological traits in Drosophila melanogaster were similar to those estimated from a conventio- nal sib analysis. Published data on isofemale strains can therefore be put into a theoretical framework. The contribution of isofemale strain analyses to the debate about the number of loci affecting variation in quantitative traits is briefly discussed.