F1 is the first filial generation: the seed of a cross between two P1 parents. In classic plant breeding the parents are two different inbred lines, so every F1 seed gets the same set of alleles from each parent. The result is a uniform, highly heterozygous crop that often shows hybrid vigour.
In practice
That uniformity is why maize and vegetable growers buy F1 hybrid seed every year. Cannabis is mostly different. Few cannabis parents are inbred, so a cross of two hybrid clones produces "F1" seed that varies a lot. Growers still call it F1 because it is the first cross, but genetically it segregates more like an F2.
True uniform cannabis F1 seed requires two inbred parents (IBLs or highly inbred lines). It exists, but it is a significant breeding investment.
Saving seed from F1 plants and growing it out gives F2s, which segregate widely. That is expected, not a fault of the seed.
Don't confuse with
- F2: offspring of F1 × F1. Wide variation.
- Feminised F1: an F1 made with reversed female pollen; still an F1, but with all-female seed.
- Hybrid: any cross between different parents. Every F1 is a hybrid; not every hybrid is a uniform F1.
Myth check
"F1 hybrid" on a pack does not guarantee uniformity unless the parents were inbred; see F1, F2, F3 explained.
Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.Heterosis (hybrid vigour) is the tendency of offspring from genetically different parents to outgrow or outperform both parents in traits such as vigour and yield.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.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.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.Feminised seed is seed made by pollinating a female with pollen from another female (or itself) that was chemically reversed, so nearly every seed grows into a female.Sex reversal is chemically inducing a genetically female cannabis plant to grow fertile male flowers, so its pollen can make feminised seed; silver thiosulfate is the standard agent.P1 is the parental generation: the two original plants crossed to start a breeding project, whose offspring are the F1.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.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.
