# Filial generation

> Filial generations (F1, F2, F3 and on) count generations of offspring from an original cross, each made by crossing plants of the previous generation together.

- Canonical: https://genetixbay.com/knowledge/glossary/filial-generation.html
- Also written: filial, F-generation, F3, F4, F5, Fn, F-number
- 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 filial generation is one step of offspring counted from an original cross. The parents are P1, their seed is the [F1](https://genetixbay.com/knowledge/glossary/f1.md), F1 × F1 gives the [F2](https://genetixbay.com/knowledge/glossary/f2.md), F2 × F2 gives the F3, and so on. The number tells you how many generations of crossing within the line have happened since the founders.

## In practice

The F-number signals how far a line is towards [breeding true](https://genetixbay.com/knowledge/glossary/true-breeding.md), but only if the breeder selected along the way. A line taken to F5 or F6 with strict selection in every generation can be close to stable for its key traits. A line taken to F5 by sowing whatever came out, with no selection, is mostly just older.

[Cannabis labels](https://genetixbay.com/knowledge/glossary/labelling-requirements.md) sometimes misuse the numbers: "F1" on a cross of two [hybrids](https://genetixbay.com/knowledge/glossary/hybrid.md), or "F5" with no records. Ask for the generation history, the number of plants grown at each step and what was selected.

## Units and formula

For a single [gene](https://genetixbay.com/knowledge/glossary/gene.md) starting [heterozygous](https://genetixbay.com/knowledge/glossary/heterozygous.md) in the F1: the F2 is 1 AA : 2 Aa : 1 aa, so 50% heterozygous. With random mating in a large population and no selection it stays near 50% in later generations; only selection and [inbreeding](https://genetixbay.com/knowledge/glossary/inbred-line.md) fix the trait. With selfing every generation it halves: 50% in F2, 25% in F3, 12.5% in F4.

## Don't confuse with

- **Backcross (BX)**: crossing back to a parent, a different route.
- **S-generation**: selfed generations (S1, S2), counted separately.
- **IBL**: an inbred line, often the end point of many filial generations with selection.

## Related terms

[P1](https://genetixbay.com/knowledge/glossary/p1.md), [F1](https://genetixbay.com/knowledge/glossary/f1.md), [F2](https://genetixbay.com/knowledge/glossary/f2.md), [IBL](https://genetixbay.com/knowledge/glossary/ibl.md), [Stabilisation](https://genetixbay.com/knowledge/glossary/stabilisation.md), [Segregation](https://genetixbay.com/knowledge/glossary/segregation.md)

## Read more

- [F1, F2, F3 explained: what filial generations really mean](https://genetixbay.com/knowledge/breeding/f1-f2-f3-explained.md)
- [Backcrossing, IBLs and stabilisation](https://genetixbay.com/knowledge/breeding/backcrossing-ibl-stabilisation.md)

## Sources

1. Allard RW. 1999. Principles of Plant Breeding, 2nd edition. John Wiley & Sons, New York. ISBN 978-0-471-02309-0