# Inbred line

> Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.

- Canonical: https://genetixbay.com/knowledge/glossary/inbred-line.html
- Also written: inbred lines, inbreeding, inbred population, inbreeding coefficient
- 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"

Inbreeding is mating between relatives: siblings, parent and offspring, or a plant with itself. It makes offspring more [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) because relatives share [alleles](https://genetixbay.com/knowledge/glossary/allele.md) inherited from common ancestors. A population produced this way is an inbred line. The degree of inbreeding is measured by the inbreeding coefficient F, the probability that both alleles at a locus are identical by descent.

## In practice

Breeders inbreed on purpose to fix traits and to make parents that pass predictable alleles. The same process exposes [recessive](https://genetixbay.com/knowledge/glossary/recessive.md) defects, so every generation needs culling. Some species tolerate inbreeding well; cannabis, an [outcrossing](https://genetixbay.com/knowledge/glossary/outcross.md) species, often shows [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md) after several generations if selection is weak.

The cannabis term [IBL](https://genetixbay.com/knowledge/glossary/ibl.md) (inbred line) usually implies a finished, stable product. "Inbred line" in general plant breeding just means any population made by inbreeding.

## Units and formula

Starting from non-inbred parents, F after one generation of: [selfing](https://genetixbay.com/knowledge/glossary/selfing.md) = 0.5; full-sib mating = 0.25; half-sib mating = 0.125. Repeated selfing: F = 1 - (1/2)^n.

## Don't confuse with

- **IBL**: the cannabis-market label for a stabilised inbred line.
- **Line breeding**: a milder form of inbreeding around a superior ancestor.
- **Clone**: copying a plant does not inbreed it; inbreeding needs sexual reproduction.

## Related terms

[IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Selfing](https://genetixbay.com/knowledge/glossary/selfing.md), [Sib cross](https://genetixbay.com/knowledge/glossary/sib-cross.md), [Line breeding](https://genetixbay.com/knowledge/glossary/line-breeding.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. Falconer DS, Mackay TFC. 1996. Introduction to Quantitative Genetics, 4th edition. Longman, Harlow. ISBN 978-0-582-24302-6
2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664