# Dominant

> A dominant allele is one whose effect shows in the phenotype even when only one copy is present, masking the other (recessive) allele at that locus.

- Canonical: https://genetixbay.com/knowledge/glossary/dominant.html
- Also written: dominance, dominant allele, complete dominance
- 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"

An [allele](https://genetixbay.com/knowledge/glossary/allele.md) is dominant when one copy is enough for its trait to show. In a heterozygous plant (Aa), the dominant allele A sets the phenotype and the [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md) a is hidden. Dominance describes how two alleles at one [locus](https://genetixbay.com/knowledge/glossary/locus.md) interact; it says nothing about whether the trait is good, common or strong.

## In practice

Dominance is why a cross can hide traits. Cross a plant carrying a dominant trait with one lacking it and every [F1](https://genetixbay.com/knowledge/glossary/f1.md) may show the dominant version. The recessive allele is still there, carried silently, and returns in about a quarter of [F2](https://genetixbay.com/knowledge/glossary/f2.md) plants (the 3:1 ratio).

[Autoflowering](https://genetixbay.com/knowledge/glossary/autoflower.md) is the classic cannabis example of the reverse case: the autoflowering trait at the Autoflower1 locus behaves as recessive, so an auto crossed to a [photoperiod plant](https://genetixbay.com/knowledge/glossary/photoperiod.md) gives photoperiod F1s (Toth et al. 2022). Breeders then need an F2 or a backcross to recover autos.

## Don't confuse with

- **Codominant**: both alleles show (THC and [CBD synthase](https://genetixbay.com/knowledge/glossary/cbda-synthase.md) at the B locus). Not a case of one masking the other.
- **Prevalent**: a dominant allele can be rare in a population; dominance is not frequency.
- **"Dominant" in strain marketing**: "indica-dominant" is a shape label, not a genetic statement.

## Related terms

[Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Codominant](https://genetixbay.com/knowledge/glossary/codominant.md), [Allele](https://genetixbay.com/knowledge/glossary/allele.md), [Heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md), [Punnett square](https://genetixbay.com/knowledge/glossary/punnett-square.md)

## Read more

- [Mendelian genetics for growers, with Punnett squares](https://genetixbay.com/knowledge/breeding/mendelian-genetics-for-growers.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. Toth JA, Stack GM, Carlson CH, Smart LB. 2022. Identification and mapping of major-effect flowering time loci Autoflower1 and Early1 in Cannabis sativa L. Frontiers in Plant Science 13:991680. https://doi.org/10.3389/fpls.2022.991680