# Pleiotropy

> Pleiotropy is when a single gene affects two or more apparently unrelated traits, so selecting on one trait changes the others too.

- Canonical: https://genetixbay.com/knowledge/glossary/pleiotropy.html
- Also written: pleiotropic, pleiotropic gene, pleiotropic effect
- 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"

Pleiotropy is when one [gene](https://genetixbay.com/knowledge/glossary/gene.md) influences several traits. Change the [allele](https://genetixbay.com/knowledge/glossary/allele.md) and you change all of them at once, whether you wanted to or not.

## In practice

Flowering-time genes are a good cannabis example. Kurtz et al. (2023) showed that the dose of the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) allele in [triploid](https://genetixbay.com/knowledge/glossary/polyploid.md) plants changed both flowering timing and plant height. Breeders working autos therefore see height and timing move together, and cannot fully separate them by selection.

Pleiotropy is one cause of correlated responses in breeding. Push hard for one trait and another drifts: a line selected only for fast finishing may lose yield; one selected only for potency may lose vigour. Good breeders track several traits at once for this reason and record what else changed.

## Don't confuse with

- **Linkage**: two separate genes near each other, inherited together. Recombination can eventually break [linkage](https://genetixbay.com/knowledge/glossary/linkage.md); it cannot separate two effects of one gene.
- **Epistasis**: two genes interacting on one trait.
- **Environment**: a correlation between traits can also come from the room, such as a hot spot that speeds finishing and cuts yield.

## Related terms

[Epistasis](https://genetixbay.com/knowledge/glossary/epistasis.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Gene](https://genetixbay.com/knowledge/glossary/gene.md), [Selection](https://genetixbay.com/knowledge/glossary/selection.md), [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.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. Kurtz LE, Brand MH, Lubell-Brand JD. 2023. Gene dosage at the autoflowering locus effects flowering timing and plant height in triploid cannabis. Journal of the American Society for Horticultural Science 148(2):83-88. https://doi.org/10.21273/JASHS05293-23
2. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6