Phenotypic variance represents the total variability observed in a trait within a population. Quantifying this variability involves partitioning it into its underlying components. This typically includes genetic variance, representing the variability due to differences in genes, and environmental variance, which accounts for the variability resulting from differences in environmental factors. The simplest calculation assumes these two components are independent and additive, resulting in phenotypic variance being the sum of genetic and environmental variances. More complex models may also include a genotype-by-environment interaction variance, reflecting instances where the effect of genotype on phenotype differs depending on the environment.
Understanding the extent of phenotypic variation is fundamental to several biological disciplines. In evolutionary biology, it provides a measure of the raw material upon which natural selection acts. In agriculture and animal breeding, it is essential for predicting the response to selection and for designing effective breeding programs. Historically, the study of phenotypic variance has roots in the development of quantitative genetics, providing frameworks to dissect the relative contributions of nature (genes) and nurture (environment) to observable traits. This knowledge enables informed decisions about strategies to improve desired traits in populations.
