# Quantitative trait

> A quantitative trait varies continuously (yield, height, flowering time, cannabinoid content) because it is controlled by many genes of small effect plus the environment.

- Canonical: https://genetixbay.com/knowledge/glossary/quantitative-trait.html
- Also written: quantitative traits, polygenic trait, complex trait, continuous trait, polygenic
- 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"

A quantitative trait is one that varies on a continuous scale rather than in a few clear classes. It is shaped by many genes, each with a small effect, and by the environment. In cannabis, yield, height, [internode length](https://genetixbay.com/knowledge/glossary/internode.md), total [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) percentage, [terpene](https://genetixbay.com/knowledge/glossary/terpene.md) content and most of flowering time are quantitative.

## In practice

Quantitative traits do not fit [Punnett squares](https://genetixbay.com/knowledge/glossary/punnett-square.md). You cannot "fix 25% THC" the way you fix a [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) leaf trait. Instead breeders measure many plants under the same conditions, estimate heritability, and shift the population average a little each generation by selecting the best parents. Progress is steady but slow, and selecting on one trait can drag others with it.

Grow-out size matters. A dozen plants tell you little about a trait whose variation is mostly environmental. Repeat measurements on clones of each candidate separate genotype from luck.

## Don't confuse with

- **Qualitative (Mendelian) trait**: falls into distinct classes controlled by one or a few genes, such as [cannabinoid chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) or autoflowering.
- **QTL**: the genomic regions that contribute to a quantitative trait.

## Myth check

[Total cannabinoid content](https://genetixbay.com/knowledge/glossary/total-cannabinoids.md) is quantitative and has a biological ceiling. Seed sold as "will hit 40%" is a marketing claim, not genetics; see [buyer beware: label claims](https://genetixbay.com/knowledge/basics/buyer-beware-label-claims.md).

## Related terms

[QTL](https://genetixbay.com/knowledge/glossary/qtl.md), [Heritability](https://genetixbay.com/knowledge/glossary/heritability.md), [Mendelian inheritance](https://genetixbay.com/knowledge/glossary/mendelian-inheritance.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Genotype by environment interaction](https://genetixbay.com/knowledge/glossary/genotype-by-environment.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
2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718