# Heterozygous

> A plant is heterozygous at a locus when it carries two different alleles there (Aa), so its offspring can inherit either one and segregate.

- Canonical: https://genetixbay.com/knowledge/glossary/heterozygous.html
- Also written: heterozygote, heterozygosity, heterozygotes, het
- 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 plant is heterozygous at a locus when its two [alleles](https://genetixbay.com/knowledge/glossary/allele.md) differ, for example Aa. Half its gametes carry A and half carry a. When heterozygous plants are crossed or selfed, their offspring segregate into different genotypes, which is why seed from a heterozygous plant varies.

## In practice

Most cannabis cultivars on the market are highly heterozygous: they are [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md) of hybrids. That is why a seed pack from two famous parents throws a spread of plants and why an [elite clone](https://genetixbay.com/knowledge/glossary/elite-cut.md)'s seed rarely reproduces the clone. The clone holds its heterozygous combination intact only because it is propagated vegetatively.

"Het" is breeder shorthand for a plant known to carry one copy of a [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md), as in "het for the auto trait". A test cross or a DNA marker can confirm it.

Heterozygosity is not a defect. High heterozygosity in [F1](https://genetixbay.com/knowledge/glossary/f1.md) hybrids is associated with [hybrid vigour](https://genetixbay.com/knowledge/glossary/heterosis.md), and wild or [landrace](https://genetixbay.com/knowledge/glossary/landrace.md) populations keep plenty of it.

## Don't confuse with

- **Homozygous**: two identical alleles.
- **Hybrid**: a cross between different parents; hybrids are usually heterozygous at many loci, but a hybrid between two different [inbred lines](https://genetixbay.com/knowledge/glossary/inbred-line.md) is uniform even so.
- **Unstable**: heterozygous plants are genetically normal; "unstable" in breeder talk means the seed line does not breed true.

## Related terms

[Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md), [Heterosis](https://genetixbay.com/knowledge/glossary/heterosis.md)

## Read more

- [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.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