A filial generation is one step of offspring counted from an original cross. The parents are P1, their seed is the F1, F1 × F1 gives the F2, 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, 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 sometimes misuse the numbers: "F1" on a cross of two hybrids, or "F5" with no records. Ask for the generation history, the number of plants grown at each step and what was selected.
For a single gene starting heterozygous 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 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.
F1 is the first generation of offspring from crossing two parents; if the parents are inbred and different, F1 plants are uniform and often show hybrid vigour.F2 is the second filial generation, made by crossing or selfing F1 plants; it shows the widest segregation, bringing back hidden recessives and new combinations.A true-breeding line produces offspring that consistently look like the parents for a given trait, because the plants are homozygous for the alleles behind it.Labelling requirements are the legal rules on what cannabis packages must and must not show, such as potency, warnings, lot number and dates.A hybrid is the offspring of two genetically different parents; almost all modern cannabis is hybrid, built from crosses between landrace-derived and other lines.A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.A plant is heterozygous at a locus when it carries two different alleles there (Aa), so its offspring can inherit either one and segregate.Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.P1 is the parental generation: the two original plants crossed to start a breeding project, whose offspring are the F1.An IBL (inbred line) is a seed line that has been inbred and selected over many generations until it breeds true for its main traits, giving uniform offspring.Stabilisation is breeding a seed line over several generations, with selection each time, until it reliably reproduces the chosen traits from seed.Segregation is the separation of a plant's two alleles at each locus into different gametes, so offspring of a heterozygous parent vary in which allele they get.
