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 again or crossed between two S1 sisters).
In practice
S1s are not clones of the parent. They reshuffle the parent's own alleles the way an F2 reshuffles an F1's, so a pack of S1s varies: some plants close to the parent, some missing key traits, some showing recessives 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 quickly. Each further S generation pushes inbreeding harder and raises the risk of inbreeding depression and unstable sex expression.
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; also all-female but not selfed.
Myth check
S1 on S1 from plants that herm 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.
Selfing is pollinating a plant with its own pollen, in cannabis usually by reversing part of a female to make pollen; it is the most intense form of inbreeding.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.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.A recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently.Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.Inbreeding depression is the loss of vigour, fertility, yield or survival that follows mating between relatives, mainly because harmful recessive alleles become homozygous.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.In cannabis growing, a plant (usually female) that develops both pistillate and staminate flowers or anthers; botanists call it intersex or monoecious expression.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.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.
