All strains labled S1 are fem. "Self seeded" shortened to S1... Which differs from "Filial generation" seed or F1, whose sex is indetermined.
F1 hybrids have a range of genetics from each parent to draw from, making pheno hunting a fun way to find a strain that embodies the characteristics of the parent you prefer. F2 is when you take a male and female from the same F1 stock to breed again. This narrows down the desired traits throughout the generations to create a more stable and consistent plant.
i.e. taking a male and female from the same seed stock that grow similar, smell similar and are overall genetically similar, will produce seeds that are more uniform and have less genetic diversity from the previous generation. And lines worked through F3, F4 and so on will produce plants that the breeders are trying ultimately trying to make. (Aficianado seeds has some stellar plants worked to the F11 generation that they make crosses with)