# Genetic drift

> Genetic drift is random change in allele frequencies between generations of a seed population, strongest in small populations; clones do not drift this way.

- Canonical: https://genetixbay.com/knowledge/glossary/genetic-drift.html
- Also written: clone drift, random genetic drift, allele drift, clone decline
- 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"

In population genetics, genetic drift is the random change in how common [alleles](https://genetixbay.com/knowledge/glossary/allele.md) are from one generation of seed to the next, caused by which plants happen to reproduce. In small populations it can lose alleles entirely or fix them by chance, regardless of whether they are useful.

## In practice

Drift matters for seed lines. Keep a line going with two or three parents per generation and it drifts quickly: alleles vanish, variation shrinks, and the line can change type without any selection. [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md) and [heirloom lines](https://genetixbay.com/knowledge/glossary/heirloom.md) stay true to their character only with enough parents each generation.

Growers also say "clone drift" for an old cut that seems to have changed. That is a different claim, and it is wrong.

## Don't confuse with

- **Selection**: non-random change, driven by the breeder's choices.
- **Somatic mutation**: rare changes in a plant's own cells. They happen (Adamek et al. 2022), but a mutation does not mean a loss, and it is not drift.
- **Topophysis**: cuts from different parts of a plant behaving differently.

## Myth check

House position: clones show zero genetic drift apart from pathogens. A cut that declines over years almost always carries a pathogen such as [hop latent viroid](https://genetixbay.com/knowledge/glossary/hop-latent-viroid.md), or suffers poor mother care. The GenetixBay founder keeps cuts 40+ years old and seed stock 50 to 70 years old with no decline. See [hop latent viroid and viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md) and [Mythbusters](https://genetixbay.com/knowledge/mythbusters.md).

## Related terms

[Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Genetic bottleneck](https://genetixbay.com/knowledge/glossary/genetic-bottleneck.md), [Founder effect](https://genetixbay.com/knowledge/glossary/founder-effect.md), [Somaclonal variation](https://genetixbay.com/knowledge/glossary/somaclonal-variation.md), [Mutation](https://genetixbay.com/knowledge/glossary/mutation.md), [Clone-only](https://genetixbay.com/knowledge/glossary/clone-only.md)

## Read more

- [Clone-only cuts and how to preserve them](https://genetixbay.com/knowledge/breeding/clone-only-preservation.md)
- [Hop latent viroid (HLVd, 'dudding') and other cannabis viruses](https://genetixbay.com/knowledge/diseases/hop-latent-viroid-and-viruses.md)

## Sources

1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6
2. Adamek K, et al. 2022. Accumulation of somatic mutations leads to genetic mosaicism in cannabis. The Plant Genome 15(1):e20169. https://doi.org/10.1002/tpg2.20169