# Outcross

> An outcross is a cross to an unrelated plant from outside the line, used to bring in new traits or vigour, or to rescue a line suffering inbreeding depression.

- Canonical: https://genetixbay.com/knowledge/glossary/outcross.html
- Also written: outcrossing, outcrossed, out-cross, wide cross
- 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"

An outcross is a mating between a plant in a breeding line and an unrelated plant from outside it. The aim is to bring in [alleles](https://genetixbay.com/knowledge/glossary/allele.md) the line lacks: a resistance, a flavour, earlier finishing, or simply fresh [heterozygosity](https://genetixbay.com/knowledge/glossary/heterozygous.md).

## In practice

Outcrossing is the standard cure for [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). A line that has been sib crossed or selfed for several generations and has lost vigour, seed set or [germination](https://genetixbay.com/knowledge/glossary/germination.md) often bounces back in a single outcross. The cost is uniformity: the outcross reshuffles everything, so the breeder usually follows it with backcrosses to the original line to recover its type while keeping the new trait.

Breeders also use "outcross" for crossing to a different population or type, for example a [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) into a modern hybrid line. That can dilute the landrace if the seed is then sold or released under the landrace's name, which is one way source-region [gene pools](https://genetixbay.com/knowledge/glossary/gene-pool.md) get contaminated.

## Don't confuse with

- **Backcross**: crossing back to a parent or the original line, the opposite direction.
- **Line breeding**: crossing within related plants; outcrossing goes outside.
- **Hybrid**: the product of any cross between different parents. An outcross produces [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) by definition.

## Related terms

[Cross](https://genetixbay.com/knowledge/glossary/cross.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.md), [Introgression](https://genetixbay.com/knowledge/glossary/introgression.md)

## Read more

- [Inbreeding depression and hybrid vigour](https://genetixbay.com/knowledge/breeding/inbreeding-depression-hybrid-vigour.md)
- [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md)

## Sources

1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0
2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664