Narrow-Sense Heritability

In the population and environment studied, 40% of observed phenotypic variance is statistically attributed to additive genetic variance: h²=VA/VP=0.4. This does not mean that 40% of an individual trait is genetically determined. Heritability describes differences among individuals in a population and can change with environment, sampling and measurement. It also does not directly predict how strongly an individual responds to an environmental change. Report the population, environment, measurement definition and estimation method. Without them, h² cannot be transferred to other groups or conditions.

Narrow-sense heritability is h²=VA/VP and considers additive genetic variance. Broad-sense heritability is H²=VG/VP and also includes dominance and epistatic components. Additive effects are often especially relevant to expected response to artificial selection because they are reliably transmitted across generations. Which measure is useful depends on the question and breeding or study design. Both remain population-specific variance ratios, not immutable properties of a trait. Report the population, environment, measurement definition and estimation method. Without them, h² cannot be transferred to other groups or conditions.

No. High heritability means that, in the population and environment studied, a large share of variation is associated with additive genetic differences. An intervention can still shift the population mean or strongly affect individual outcomes. If environments become more uniform, the heritability proportion can even rise while genes remain unchanged. Intervention decisions need causal evidence and absolute changes; h² alone is neither an individual prediction nor a policy recommendation. Report the population, environment, measurement definition and estimation method. Without them, h² cannot be transferred to other groups or conditions.

Reproduce the example calculation: In a defined sample, suppose VA=20 cm² and VP=80 cm². Narrow-Sense Heritability uses h² = VA/VP. In plain terms, narrow-sense heritability is the fraction of phenotypic variance attributable to additive genetic variance in a specified population and environment. Unit check: h² dimensionless, usually 0–1 · VA and VP are variances in squared trait units. Variance components apply to a defined trait, population, environment and design; gene–environment covariance can violate simple decompositions. Values are comparable only when their definitions, denominators and periods match. Record these details next to the result so the reference group is clear. If the direction is implausible, check data preparation and the calculation basis before discussing biological causes.

A key limit of Narrow-Sense Heritability is this: Variance components apply to a defined trait, population, environment and design; gene–environment covariance can violate simple decompositions. Do not use the metric without its reference; it is useful for Quantitative genetics, population comparisons and response-to-selection models when population, trait and environment are specified. Narrow-sense heritability is the fraction of phenotypic variance attributable to additive genetic variance in a specified population and environment. When comparing populations or experiments, check whether definitions, denominators and observation periods match. If the assumption is implausible, the result shows only what the simplified model calculates from its inputs; it is not a reliable estimate for the target population. State this limitation in the report, and do not infer a causal effect from the formula alone.