• Quantitative genetics, which is concerned with characters controlled by many genes, considers the changes in phenotypic and genotypic frequency distributions between generations, rather than following the fate of individual genes.

• The phenotypic variance of a character in a population can be divided into components due to genetic, and to environmental, differences between individuals.

• Some of the genetic effects on an individual's phenotype are inherited by its offspring; others are not. The former are called additive genetic effects; the latter are due to such factors as dominance and epistatic interaction between genes.

• The heritability of a character is the proportion of its total phenotypic variance in a population that is additive.

• The heritability of a character determines its evolutionary response to selection.

• The additive genetic variance can be measured by the correlation between relatives, or by artificial selection experiments.

• The response of a population to artificial selection depends on the amount of additive genetic variability and on the relation between genotype and phenotype.