# S1

> S1 is seed from a plant pollinated with its own pollen; every S1 seed is female and a new genotype, not a copy of the parent.

- Canonical: https://genetixbay.com/knowledge/glossary/s1.html
- Also written: S1 seed, S1s, S2, S2 seed, selfed seed, first selfed generation, S1 generation
- 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"

S1 is the first selfed generation: seed from a plant fertilised by its own pollen. In cannabis it is made by reversing a branch or clone of a female and using that pollen on the same genotype. S1s are female, because both gametes carry X. S2 is the next generation, S1 × S1 of the same line ([selfed](https://genetixbay.com/knowledge/glossary/selfing.md) again or crossed between two S1 sisters).

## In practice

S1s are not clones of the parent. They reshuffle the parent's own [alleles](https://genetixbay.com/knowledge/glossary/allele.md) the way an F2 reshuffles an [F1](https://genetixbay.com/knowledge/glossary/f1.md)'s, so a pack of S1s varies: some plants close to the parent, some missing key traits, some showing [recessives](https://genetixbay.com/knowledge/glossary/recessive.md) the parent hid. At each heterozygous locus, about half the S1s become homozygous.

People make S1s to preserve something of a clone in seed form, to test what a clone carries, or to start an [inbred line](https://genetixbay.com/knowledge/glossary/inbred-line.md) quickly. Each further S generation pushes inbreeding harder and raises the risk of [inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md) and unstable sex expression.

## Units and formula

Inbreeding coefficient: S1 F = 0.5, S2 F = 0.75, S3 F = 0.875 (starting from a non-inbred parent).

## Don't confuse with

- **Clone**: an exact copy, made by cuttings. S1 is seed.
- **Feminised cross**: female × different [reversed female](https://genetixbay.com/knowledge/glossary/sex-reversal.md); also all-female but not selfed.

## Myth check

S1 on S1 from plants that [herm](https://genetixbay.com/knowledge/glossary/hermaphrodite.md) is a main route to herm-prone lines. House position: selfing is mostly frowned upon; self only proven-stable females and cull every intersex offspring. See [S1s and selfing](https://genetixbay.com/knowledge/breeding/s1-selfing.md).

## Related terms

[Selfing](https://genetixbay.com/knowledge/glossary/selfing.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Inbreeding depression](https://genetixbay.com/knowledge/glossary/inbreeding-depression.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md)

## Read more

- [S1s and selfing: what happens when a plant pollinates itself](https://genetixbay.com/knowledge/breeding/s1-selfing.md)
- [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md)

## Sources

1. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718
2. Charlesworth D, Willis JH. 2009. The genetics of inbreeding depression. Nature Reviews Genetics 10:783-796. https://doi.org/10.1038/nrg2664