# Introgression

> Introgression is the movement of genes from one population or type into another through hybridisation followed by repeated backcrossing.

- Canonical: https://genetixbay.com/knowledge/glossary/introgression.html
- Also written: introgressed, introgressive hybridisation, introgressive hybridization, gene flow, trait introgression
- 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"

Introgression is the transfer of [genetic material](https://genetixbay.com/knowledge/glossary/germplasm.md) from one population into another, through a cross followed by repeated [backcrossing](https://genetixbay.com/knowledge/glossary/backcross.md) to the receiving population. The result is a population that is mostly the recipient but carries segments of the donor's DNA.

## In practice

Breeders introgress traits on purpose: move the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) [allele](https://genetixbay.com/knowledge/glossary/allele.md), a disease resistance or a chemotype into an [elite](https://genetixbay.com/knowledge/glossary/elite-cut.md) line by crossing then backcrossing several times. The CBD-producing alleles in many drug-type cannabis lines appear to come from [hemp](https://genetixbay.com/knowledge/glossary/hemp.md) introgressed into marijuana (Grassa et al. 2021).

Introgression also happens unintentionally. When imported hybrid seed is grown near traditional fields, its pollen enters the local [landrace](https://genetixbay.com/knowledge/glossary/landrace.md). Over generations the landrace carries more and more foreign DNA and loses its distinct type. That is one documented route by which source-region landraces are being diluted.

## Don't confuse with

- **Backcross**: the breeding step; introgression is the overall movement of genes.
- **Hybrid**: the first cross; introgression requires further generations.
- **Contamination (seed purity)**: stray pollen in a [seed run](https://genetixbay.com/knowledge/glossary/seed-run.md); it can start introgression if the seed is kept.

## Related terms

[Backcross](https://genetixbay.com/knowledge/glossary/backcross.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md), [Landrace](https://genetixbay.com/knowledge/glossary/landrace.md), [Gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md), [Outcross](https://genetixbay.com/knowledge/glossary/outcross.md)

## Read more

- [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.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. Grassa CJ, Weiblen GD, Wenger JP, et al. 2021. A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist 230(4):1665-1679. https://doi.org/10.1111/nph.17243
2. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718