Heritability and Gene-Environment Interaction

Heritability is a population statistic that expresses the proportion of variation in a trait, within a particular population and environment, that can be attributed to genetic differences among individuals. Gene-environment interaction refers to the way the effect of a genetic variant on a trait can depend on the environment, and vice versa. Together they frame how genetics partitions trait variation while cautioning against over-reading what that partition means for any single person.

Definition

Heritability is the fraction of phenotypic variance in a defined population attributable to genetic variance; narrow-sense heritability counts only additive genetic variance, while broad-sense heritability counts all genetic variance. Gene-environment interaction occurs when the effect of genotype on phenotype differs across environments.

Scope

The entry covers the definition and estimation of heritability (including narrow- and broad-sense), the meaning and common misinterpretations of the statistic, gene-environment interaction and correlation, and how genomic methods estimate heritability from genetic data. It is a conceptual and methodological topic, not clinical guidance.

Core questions

• What exactly does a heritability estimate measure, and to what population does it apply?
• Why does heritability say nothing direct about an individual or about whether a trait can be changed?
• How do gene-environment interaction and gene-environment correlation complicate the partition of variance?
• How is heritability estimated from family data versus from genome-wide genetic data?

Key concepts

• Narrow-sense heritability (additive)
• Broad-sense heritability
• Phenotypic variance partition
• SNP-based heritability
• Gene-environment interaction
• Gene-environment correlation
• Population- and environment-specific estimate

Key theories

Variance partitioning

Fisher's framework decomposes phenotypic variance into genetic and environmental components, providing the formal basis for defining heritability as the ratio of genetic to total phenotypic variance and for separating additive from non-additive genetic effects.

Mechanisms

Heritability is computed by partitioning the variance of a trait across individuals into genetic and environmental components; the genetic share, relative to the total, defines heritability. Family and twin designs infer this from the resemblance of relatives, while genomic methods estimate it from measured genetic similarity across many variants. Because it is a ratio of variances, heritability depends on the allele frequencies and the range of environments present in the studied population, and it can shift if either changes. Gene-environment interaction means a variant's apparent effect can differ between environments, and gene-environment correlation means genotypes may be non-randomly distributed across environments; both must be considered when interpreting variance components.

Clinical relevance

Heritability and gene-environment interaction inform how genetic evidence about common traits and diseases is interpreted, including why a high heritability does not imply that environmental or behavioural factors are unimportant or fixed. The material is presented to support critical reading of genetic evidence at the population level and is not a basis for individual prediction or care.

Epidemiology

Heritability estimates have been produced for a very wide range of human traits and common diseases, typically through twin and family studies and, more recently, genome-wide genetic data; estimates vary by trait, population, and environment, which is itself an important interpretive point.

History

The concept follows from Fisher's 1918 variance-partitioning framework and was developed for practical estimation by quantitative geneticists such as Falconer. In the genomics era, methods that estimate heritability directly from genome-wide variants — applied first to traits such as human height — both quantified the genetic share captured by common variants and sharpened debate over the gap between this and family-based heritability.

Debates

What does heritability tell us, and what does it not?

Heritability is frequently misread as a measure of how 'genetic' a trait is in an individual or as fixed across settings; in fact it is a population- and environment-specific ratio of variances, and its limits are a recurrent theme in the literature.

Why is family-based heritability often higher than the heritability captured by measured variants?

Genomic estimates from common variants frequently fall short of family-based heritability, with proposed reasons including undetected variants, rare variation, interactions, and possible overestimation by family designs.

Key figures

• Ronald A. Fisher
• Douglas Falconer
• Peter Visscher
• Jian Yang

Seminal works

• fisher-1918
• visscher-2008
• yang-2010

Frequently asked questions

Does a heritability of 80% mean a trait is 80% genetic in me?

No. Heritability describes the share of variation among people in a population that tracks genetic differences in a given environment; it does not partition cause within any single individual.

What is gene-environment interaction?

It is when the effect of a genetic variant on a trait depends on the environment — for example, a variant might raise risk only under a particular exposure — so genotype and environment cannot always be treated as simply additive.