# Sib cross

> A sib cross is a cross between siblings from the same seed batch, used to advance a line (F1 × F1 gives F2) while keeping it within the family.

- Canonical: https://genetixbay.com/knowledge/glossary/sib-cross.html
- Also written: sibling cross, sibbing, full-sib cross, half-sib cross, sib mating
- 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 sib cross is a cross between siblings. Full sibs share both parents; half sibs share one. In cannabis it usually means crossing a selected female with a selected male from the same [seed batch](https://genetixbay.com/knowledge/glossary/seed-run.md), which is how [F2](https://genetixbay.com/knowledge/glossary/f2.md), [F3](https://genetixbay.com/knowledge/glossary/filial-generation.md) and later generations are made.

## In practice

Sib crossing is the standard way to advance a line without bringing in outside genetics. With selection each generation, it gradually raises [homozygosity](https://genetixbay.com/knowledge/glossary/homozygous.md) and makes the line more uniform. It is slower and gentler than [selfing](https://genetixbay.com/knowledge/glossary/selfing.md).

Done with tiny populations (one female, one male, every generation), sib crossing narrows the [gene pool](https://genetixbay.com/knowledge/glossary/gene-pool.md) quickly and can lead to [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). Breeders reduce this by selecting from more plants, keeping several parallel families, and crossing families occasionally.

Unlike selfing, a sib cross uses a real male. GenetixBay prefers it for exactly that reason: males are part of breeding, and a selected male carries information the female alone cannot.

## Units and formula

[Inbreeding coefficient](https://genetixbay.com/knowledge/glossary/inbred-line.md) after one generation of full-sib mating from unrelated parents: F = 0.25. Half-sib: F = 0.125.

## Don't confuse with

- **Selfing**: the same plant as both parents (F = 0.5 in one generation).
- **Outcross**: crossing outside the family.

## Related terms

[F2](https://genetixbay.com/knowledge/glossary/f2.md), [Filial generation](https://genetixbay.com/knowledge/glossary/filial-generation.md), [Inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md)

## Read more

- [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md)

## Sources

1. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6
2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0