# Backcross

> A backcross is a cross of a hybrid back to one of its parents (or that parent's line), repeated to recover the parent's traits while keeping one introduced trait.

- Canonical: https://genetixbay.com/knowledge/glossary/backcross.html
- Also written: BX, BC, backcrossing, BX1, BX2, BX3, back cross, cubing, cubed
- 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 backcross (BX or BC) crosses an offspring back to one of its parents, called the recurrent parent. Each round raises the expected share of the recurrent parent's genome. Breeders use repeated backcrossing to move one trait from a donor into an [elite](https://genetixbay.com/knowledge/glossary/elite-cut.md) line while keeping the elite line's type.

## In practice

Example: an elite female clone is crossed to a male carrying the [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) trait. A male from the offspring is crossed back to the same female (BX1), then a selected BX1 male back to her again (BX2), then BX3. Each time the breeder selects offspring that carry the wanted trait and otherwise look like the clone.

"Cubing" is cannabis slang for three backcrosses to a female clone, from the idea of raising her share to the third power. It approaches the clone's [genotype](https://genetixbay.com/knowledge/glossary/genotype.md) but never reproduces her exactly, and [linkage drag](https://genetixbay.com/knowledge/glossary/linkage.md) means some donor DNA around the selected trait comes along.

## Units and formula

Expected recurrent-parent share after n backcrosses (starting from an [F1](https://genetixbay.com/knowledge/glossary/f1.md) at 50%): 1 - (1/2)^(n+1). BX1: 75%; BX2: 87.5%; BX3: 93.75%; BX4: about 96.9%.

## Don't confuse with

- **Selfing**: [pollinating](https://genetixbay.com/knowledge/glossary/pollination.md) a plant with its own pollen. A backcross uses a different plant (the offspring) as the other parent.
- **Outcross**: crossing to an unrelated plant.
- **Clone**: a backcross line is never identical to the recurrent parent; only a cutting is.

## Related terms

[IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Introgression](https://genetixbay.com/knowledge/glossary/introgression.md), [P1](https://genetixbay.com/knowledge/glossary/p1.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Linkage](https://genetixbay.com/knowledge/glossary/linkage.md)

## Read more

- [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. Acquaah G. 2012. Principles of Plant Genetics and Breeding, 2nd edition. Wiley-Blackwell. https://doi.org/10.1002/9781118313718