# Genetic bottleneck

> A genetic bottleneck is a sharp drop in the number of breeding plants, after which the population carries only a fraction of its former genetic diversity.

- Canonical: https://genetixbay.com/knowledge/glossary/genetic-bottleneck.html
- Also written: bottleneck, population bottleneck, bottlenecked, bottleneck 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"

A genetic bottleneck happens when a population is reduced to very few breeding individuals. Only the [alleles](https://genetixbay.com/knowledge/glossary/allele.md) carried by the survivors pass on; rare alleles are often lost, and the population afterwards is more inbred and less variable, even if it later grows large again.

## In practice

Cannabis has passed through many bottlenecks. [Landraces](https://genetixbay.com/knowledge/glossary/landrace.md) carried out of source regions in a single seed packet; a whole line rebuilt from three plants after a raid or crop loss; a modern cultivar group descended mostly from a handful of famous clones. Each step narrows what breeders have to work with.

Breeders create bottlenecks themselves by making each generation from one female and one male. The cure is [prevention](https://genetixbay.com/knowledge/glossary/cultural-control.md): use many parents, keep backup seed, and preserve material from different sources.

## Don't confuse with

- **Founder effect**: a special case, when a new population is started by a few individuals.
- **Genetic drift**: random change in allele frequency; it is strongest during and after a bottleneck.
- **Selection**: keeping plants on purpose for traits; a bottleneck is a loss in numbers, chosen or not.

## Related terms

[Founder effect](https://genetixbay.com/knowledge/glossary/founder-effect.md), [Genetic drift](https://genetixbay.com/knowledge/glossary/genetic-drift.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Germplasm](https://genetixbay.com/knowledge/glossary/germplasm.md)

## Read more

- [Patents and the gene pool: who can own a cannabis plant?](https://genetixbay.com/knowledge/genetics-history/patents-and-the-gene-pool.md)
- [Why everything tastes the same: the evidence that commercial cannabis is converging](https://genetixbay.com/knowledge/genetics-history/why-everything-tastes-the-same.md)

## Sources

1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6
2. Clarke RC, Merlin MD. 2013. Cannabis: Evolution and Ethnobotany. University of California Press. https://doi.org/10.1525/9780520954571