# True breeding

> A true-breeding line produces offspring that consistently look like the parents for a given trait, because the plants are homozygous for the alleles behind it.

- Canonical: https://genetixbay.com/knowledge/glossary/true-breeding.html
- Also written: breeds true, breeding true, true-to-type, true to type, pure-breeding
- 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 [line breeds](https://genetixbay.com/knowledge/glossary/line-breeding.md) true for a trait when its offspring reliably show that trait, generation after generation. Genetically, every plant is [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) for the relevant [alleles](https://genetixbay.com/knowledge/glossary/allele.md), so there is nothing left to segregate. Mendel's pea lines were true-breeding before he crossed them.

## In practice

True breeding is trait by trait. An inbred cannabis line may breed true for [chemotype](https://genetixbay.com/knowledge/glossary/chemotype.md) and flowering time and still vary for aroma or yield. A balanced 1:1 THC:CBD plant can never breed true from seed because its chemotype comes from being [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md); crossing two of them gives the 1:2:1 split.

Breeders test it with a grow-out of enough seed. If every plant in 30 or more matches the target for the trait, the line is very likely true-breeding for it. Clones are always true to type for every trait, because they are copies, not offspring.

## Don't confuse with

- **True to type (clone)**: a cutting matches its mother. In seed, "true to type" means the line breeds true.
- **Uniformity**: often a sign of true breeding, but an [F1](https://genetixbay.com/knowledge/glossary/f1.md) of two [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md) is uniform and still does not breed true in the next generation.
- **Stable sex**: a separate quality. True breeding for aroma says nothing about [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md).

## Related terms

[Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Uniformity](https://genetixbay.com/knowledge/glossary/uniformity.md), [Open-pollinated](https://genetixbay.com/knowledge/glossary/open-pollinated.md)

## Read more

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

## Sources

1. Miko I. 2008. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593/
2. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0