Define heritability in quantitative genetics.

• A. The proportion of phenotypic variation in a trait due to genetic variation.
• B. The total genetic influence on a trait.
• C. The proportion of a trait determined by environment.
• D. The rate at which genes are inherited.

Answer: (A)

Heritability tells us how much of the differences we see in a trait among individuals in a population come from genetic differences rather than environmental differences. It's a population-level measure, not a prediction about any single person, and it can change depending on the population and environment. It’s expressed as a ratio: h^2 equals the genetic variance divided by the total phenotypic variance (V_G / V_P). A higher heritability means genetics account for most of the observable variation under the current conditions, while a lower value means the environment plays a larger role. The other descriptions miss the point: one talks about the total genetic influence (not a proportion), another about the environmental portion, and another about the rate of gene transmission, which isn’t what heritability measures.