# Heterosis

> Heterosis (hybrid vigour) is the tendency of offspring from genetically different parents to outgrow or outperform both parents in traits such as vigour and yield.

- Canonical: https://genetixbay.com/knowledge/glossary/heterosis.html
- Also written: hybrid vigour, hybrid vigor, heterotic, F1 vigour, hybrid vitality
- 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"

Heterosis, or hybrid vigour, is when the offspring of two genetically different parents performs better than the average of the parents, or better than the best parent, for traits like growth rate, size, yield or stress tolerance. It is the mirror image of [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md).

## In practice

Heterosis is strongest when two distinct, inbred parents are crossed: the [F1](https://genetixbay.com/knowledge/glossary/f1.md) is uniform and vigorous. Maize breeding is built on it. In cannabis, growers notice it as F1 seedlings that race away compared with either parent, or a fresh [outcross](https://genetixbay.com/knowledge/glossary/outcross.md) that rescues a tired line.

It fades in the [F2](https://genetixbay.com/knowledge/glossary/f2.md). Crossing F1 plants with each other reshuffles the [alleles](https://genetixbay.com/knowledge/glossary/allele.md), so part of the vigour is lost and the population becomes variable again. That is why F1 seed is normally remade each time from the parents.

The causes are still debated: masking of deleterious [recessives](https://genetixbay.com/knowledge/glossary/recessive.md) (dominance), favourable allele interactions, and gene-regulation effects all contribute (Schnable and Springer 2013).

## Don't confuse with

- **Heterozygosity**: a genetic state; heterosis is a performance outcome. [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) plants are not automatically vigorous.
- **Stretch**: fast vertical growth from light or temperature, not hybrid vigour.
- **Quality**: a vigorous F1 is not necessarily higher in [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md) or flavour.

## Related terms

[F1](https://genetixbay.com/knowledge/glossary/f1.md), [Hybrid](https://genetixbay.com/knowledge/glossary/hybrid.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Outcross](https://genetixbay.com/knowledge/glossary/outcross.md), [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md)

## Read more

- [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md)

## Sources

1. Schnable PS, Springer NM. 2013. Progress toward understanding heterosis in crop plants. Annual Review of Plant Biology 64:71-88. https://doi.org/10.1146/annurev-arplant-050312-120145
2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664