# Heritability

> Heritability is the share of a trait's variation within a population that is due to genetic differences rather than environment, on a scale from 0 to 1.

- Canonical: https://genetixbay.com/knowledge/glossary/heritability.html
- Also written: heritable, h2, broad-sense heritability, narrow-sense heritability
- Glossary category: Genetics and breeding · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Heritability is the proportion of the observed variation in a trait, in one population and one set of conditions, that is explained by genetic differences. It runs from 0 (all differences are environmental) to 1 (all are genetic). Broad-sense heritability (H²) counts all genetic effects; narrow-sense (h²) counts only the additive part, which is what predicts response to selection.

## In practice

High-heritability traits respond quickly to selection: pick the best parents and the offspring follow. Flowering time and the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type behave like this. Low-heritability traits (yield per plant is the classic) are dominated by environment and plant position, so selecting the biggest plant in a tent often picks the luckiest spot, not the best [genes](https://genetixbay.com/knowledge/glossary/gene.md).

That is why good breeders grow candidates in uniform conditions, repeat them as clones, and judge parents by their offspring.

## Units and formula

H² = VG / VP and h² = VA / VP, where VP is total phenotypic variance, VG genetic variance and VA additive genetic variance. Response to selection: R = h² × S (the breeder's equation), where S is how far the selected parents are above the population mean.

## Don't confuse with

- **Inherited**: a trait can be fully genetic yet show zero heritability in a uniform population, because there is no variation left.
- **Fixed number**: heritability belongs to a population and an environment; change either and it changes.

## Related terms

[Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.md), [Progeny test](https://genetixbay.com/knowledge/glossary/progeny-test.md)

## Read more

- [Quantitative traits and heritability: why most good traits are hard to fix](https://genetixbay.com/knowledge/breeding/quantitative-traits-heritability.md)

## Sources

1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6