New Zealand lamb breeders measure the following variance values for their herd. Trait VP VG VA Body mass (kg) 42.4 20.5 7.4 Body fat (%) 38.9 16.2 5.7 Body length (cm) 51.6 26.4 8.1 How would you characterize the potential response to selection (R) for each trait?

Key Concepts

Phenotypic Variance (VP)

Phenotypic variance (VP) refers to the total variance observed in a trait within a population, which is influenced by both genetic and environmental factors. It is calculated as the sum of genetic variance (VG) and environmental variance (VE). Understanding VP is crucial for predicting how traits may respond to selection, as it provides a baseline for assessing the variability that can be acted upon by selective pressures.

Genetic Variance (VG)

Genetic variance (VG) is the portion of phenotypic variance that is attributable to genetic differences among individuals in a population. It can be further divided into additive genetic variance (VA), which contributes to the average response to selection, and non-additive variance. A higher VG indicates a greater potential for a trait to respond to selection, making it essential for breeders to understand when evaluating traits for improvement.

Response to Selection (R)

Response to selection (R) is the change in the mean phenotype of a trait in a population following selection. It is influenced by the heritability of the trait, which is the ratio of additive genetic variance to phenotypic variance. The formula R = h²S, where S is the selection differential, helps predict how much a trait will change in response to selection, making it a key concept for breeders aiming to enhance specific traits in livestock.