# Mendelian inheritance

> Mendelian inheritance is the pattern in which single genes pass from parents to offspring in predictable ratios, following Mendel's laws of segregation and independent assortment.

- Canonical: https://genetixbay.com/knowledge/glossary/mendelian-inheritance.html
- Also written: Mendelian genetics, Mendel's laws, Mendelian ratios, Mendelism, simple inheritance
- 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"

Mendelian inheritance is the pattern by which single [genes](https://genetixbay.com/knowledge/glossary/gene.md) pass to offspring in predictable ratios. Gregor Mendel described it from pea crosses in 1866: each parent passes one of its two alleles per gene at random ([segregation](https://genetixbay.com/knowledge/glossary/segregation.md)), and genes on different chromosomes are inherited independently ([independent assortment](https://genetixbay.com/knowledge/glossary/independent-assortment.md)).

## In practice

Mendelian ratios are the breeder's first tool. A single-gene trait with a [dominant](https://genetixbay.com/knowledge/glossary/dominant.md) and a [recessive allele](https://genetixbay.com/knowledge/glossary/recessive.md) gives a 3:1 visible ratio in the F2 and 1:1 in a [test cross](https://genetixbay.com/knowledge/glossary/test-cross.md). Cannabis traits that behave roughly this way include the [cannabinoid](https://genetixbay.com/knowledge/glossary/cannabinoid.md) synthase type (codominant, de Meijer et al. 2003), autoflowering (recessive) and some leaf and colour traits.

Most traits growers care about are not Mendelian. Yield, vigour, resin coverage, total cannabinoid percentage and flowering time are quantitative: many genes of small effect plus the environment. For those, [Punnett squares](https://genetixbay.com/knowledge/glossary/punnett-square.md) mislead and breeders work with heritability, large populations and repeated selection.

## Units and formula

One gene (Aa × Aa): 1 AA : 2 Aa : 1 aa, visible 3:1 if A is dominant. Two independent genes (AaBb × AaBb): visible 9:3:3:1. Test cross (Aa × aa): 1:1.

## Don't confuse with

- **Quantitative inheritance**: continuous variation from many genes.
- **Linkage**: genes close together on one chromosome break the independent-assortment rule.

## Related terms

[Segregation](https://genetixbay.com/knowledge/glossary/segregation.md), [Independent assortment](https://genetixbay.com/knowledge/glossary/independent-assortment.md), [Punnett square](https://genetixbay.com/knowledge/glossary/punnett-square.md), [Dominant](https://genetixbay.com/knowledge/glossary/dominant.md), [Recessive](https://genetixbay.com/knowledge/glossary/recessive.md), [Quantitative trait](https://genetixbay.com/knowledge/glossary/quantitative-trait.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. de Meijer EPM, Bagatta M, Carboni A, et al. 2003. The inheritance of chemical phenotype in Cannabis sativa L. Genetics 163(1):335-346. https://doi.org/10.1093/genetics/163.1.335