# Recessive

> A recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently.

- Canonical: https://genetixbay.com/knowledge/glossary/recessive.html
- Also written: recessive allele, recessive trait, recessives
- 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 recessive allele shows in the [phenotype](https://genetixbay.com/knowledge/glossary/phenotype.md) only when the plant is [homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md) for it (aa). A plant with one copy (Aa) looks like the [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) type but passes the recessive allele to about half its offspring.

## In practice

Recessives are why seed lines surprise people. Two vigorous parents can both carry a hidden recessive for weak growth, odd leaves or a missing trait; about one in four of their offspring will show it. Selfing and close [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) bring recessives out fast because they push loci towards homozygosity. That works both ways: it can reveal a rare recessive aroma a breeder wants to fix, or a defect that has to be culled.

The [autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) trait is recessive. So is the expression of many deleterious [alleles](https://genetixbay.com/knowledge/glossary/allele.md) that cause [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md). A breeder who wants to know whether a plant carries a recessive does a [test cross](https://genetixbay.com/knowledge/glossary/test-cross.md) with a known aa plant: any aa offspring prove the carrier.

## Don't confuse with

- **Rare**: a recessive allele can be common in a population and still be hidden in most plants.
- **Weak or bad**: recessive describes inheritance, not value. Many desirable traits are recessive.
- **Codominant**: in codominance both alleles show; nothing is hidden.

## Related terms

[Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Homozygous](https://genetixbay.com/knowledge/glossary/homozygous.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md)

## Read more

- [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.md)
- [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.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. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664