# XY sex determination

> Cannabis uses an XY sex determination system: females carry two X chromosomes (XX) and males an X and a Y (XY), so regular seed is roughly half male.

- Canonical: https://genetixbay.com/knowledge/glossary/xy-sex-determination.html
- Also written: XY system, sex chromosomes, X and Y chromosomes, XX female, XY male
- 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"

Cannabis has an XY sex determination system. Females are XX; males are XY. The Y [chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md) is the larger of the pair, and its region that does not recombine with the X carries the male-determining genes (Divashuk et al. 2014; Prentout et al. 2020).

## In practice

Regular seed comes from a female (XX) pollinated by a male (XY). Each seed gets an X from the mother and either X or Y from the father, so regular [seed runs](https://genetixbay.com/knowledge/glossary/seed-run.md) close to 50:50 female to male. Males can be identified early with a DNA sex test on a leaf sample (Toth et al. 2020), saving months of veg space.

[Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md) works because of this system. A female reversed with [silver thiosulfate](https://genetixbay.com/knowledge/glossary/sts.md) makes pollen that carries only X chromosomes. Every seed from that pollen is XX. Sex expression can still be disturbed in genetically weak lines, which is why stable feminised seed depends on reversing only proven-stable [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md).

## Don't confuse with

- **Hermaphrodite**: a plant that shows both flower types. It is a sex-expression failure, not a third chromosome type.
- **Monoecious hemp**: bred deliberately to carry both flowers on one plant; drug-type cannabis is [dioecious](https://genetixbay.com/knowledge/glossary/dioecious.md).

## Myth check

Cannabis has been recorded as dioecious throughout history. [Herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) lines are mainly breeder error, not the plant's nature; see [male, female and hermaphrodite](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md).

## Related terms

[Chromosome](https://genetixbay.com/knowledge/glossary/chromosome.md), [Regular seed](https://genetixbay.com/knowledge/glossary/regular-seed.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Male selection](https://genetixbay.com/knowledge/glossary/male-selection.md)

## Read more

- [Male, female and hermaphrodite cannabis: how sex works](https://genetixbay.com/knowledge/basics/sex-male-female-hermaphrodite.md)
- [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md)

## Sources

1. Divashuk MG, Alexandrov OS, Razumova OV, Kirov IV, Karlov GI. 2014. Molecular cytogenetic characterization of the dioecious Cannabis sativa with an XY chromosome sex determination system. PLoS ONE 9(1):e85118. https://doi.org/10.1371/journal.pone.0085118
2. Prentout D, Razumova O, Rhone B, et al. 2020. An efficient RNA-seq-based segregation analysis identifies the sex chromosomes of Cannabis sativa. Genome Research 30(2):164-172. https://doi.org/10.1101/gr.251207.119
3. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667