--- title: "Quantitative Traits, Variance Components and Heritability" description: "Traits governed by many genes vary continuously, and the observed variance can be split into genetic and environmental parts. Heritability is the share of variance that is genetic in one population an" canonical: https://lightmysky.com/learn/science/quantitative-traits-variance-components-and-heritability-mt_orJhIlYnKM source: https://lightmysky.com/learn/science/quantitative-traits-variance-components-and-heritability-mt_orJhIlYnKM.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Quantitative Traits, Variance Components and Heritability Traits governed by many genes vary continuously, and the observed variance can be split into genetic and environmental parts. Heritability is the share of variance that is genetic in one population and one environment, which is not the same as how much of the trait is inherited. Subject: Science · Area: Genetics & Evolution · Ages 18 to 20 Page: https://lightmysky.com/learn/science/quantitative-traits-variance-components-and-heritability-mt_orJhIlYnKM ## Ready when they can - Splits a stated total variance into its components and calculates heritability. - Explains why heritability changes when the environment changes, with the population unchanged. - Rejects the reading that a heritability of 0.6 means sixty per cent of an individual's trait comes from genes. ## Lesson: Why continuous traits need variance Traits like height vary smoothly because many genes each add a small push and the setting pushes back. The result is a bell shaped curve, not neat Mendelian classes. Analysis then shifts from single genotypes to variance across a whole population. **Example.** Total variance splits into genetic and environmental parts. Say genetic variance is 60 and environmental variance is 40, so total variance is 100. Broad sense heritability is 60 divided by 100, which is 0.6. Narrow sense uses only the additive part, the part that answers selection. A heritability of 0.6 says 60 percent of the variation in that one population comes from genetic differences. It never says 60 percent of any single person comes from genes. Change the setting and heritability moves: uniform surroundings raise it, varied surroundings lower it, with no genetic change at all. **Tip.** Always name the population and the setting before quoting a heritability. Two groups with the same alleles can look different if one is better fed. Selection can shift one group and stall in another for the same reason. **Recap.** Split variance into genetic and environmental parts, and read heritability as a population number tied to one setting. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Epistasis and Reading Pathway Order from Double Mutants](https://lightmysky.com/learn/science/epistasis-and-reading-pathway-order-from-double-mutants-mt_eE2WRPyYPk) ## Opens up - [Association Studies and What They Can and Cannot Show](https://lightmysky.com/learn/science/association-studies-and-what-they-can-and-cannot-show-mt_IFFUFX3xrv) - [Selection on Quantitative Traits and Predicting the Response](https://lightmysky.com/learn/science/selection-on-quantitative-traits-and-predicting-the-response-mt_M-czTLDmfl)