Cannabis has an XY sex determination system. Females are XX; males are XY. The Y chromosome is the larger of the pair, and its region that does not recombine with the X carries the male-determining genes (Divashuk et al. 2014; Prentout et al. 2020).
In practice
Regular seed comes from a female (XX) pollinated by a male (XY). Each seed gets an X from the mother and either X or Y from the father, so regular seed runs close to 50:50 female to male. Males can be identified early with a DNA sex test on a leaf sample (Toth et al. 2020), saving months of veg space.
Feminised seed works because of this system. A female reversed with silver thiosulfate makes pollen that carries only X chromosomes. Every seed from that pollen is XX. Sex expression can still be disturbed in genetically weak lines, which is why stable feminised seed depends on reversing only proven-stable mothers.
Don't confuse with
- Hermaphrodite: a plant that shows both flower types. It is a sex-expression failure, not a third chromosome type.
- Monoecious hemp: bred deliberately to carry both flowers on one plant; drug-type cannabis is dioecious.
Myth check
Cannabis has been recorded as dioecious throughout history. Herm-prone lines are mainly breeder error, not the plant's nature; see male, female and hermaphrodite.
A chromosome is one long DNA molecule packaged with proteins that carries many genes; cannabis normally has 10 pairs, nine autosome pairs plus an X/Y sex pair.A seed run is a dedicated grow in which selected parents are crossed to produce a batch of seed, as opposed to growing for flower.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.STS (silver thiosulfate) is a silver compound sprayed on female cannabis to block ethylene action and induce fertile male flowers, the standard method for making feminised seed.A mother plant is a female kept permanently in vegetative growth to supply cuttings, so a selected genotype can be propagated as clones indefinitely.In cannabis growing, a plant (usually female) that develops both pistillate and staminate flowers or anthers; botanists call it intersex or monoecious expression.Having male and female flowers on separate individual plants; drug-type cannabis is naturally dioecious with an XY sex-chromosome system.Herm-prone describes a line whose plants often produce intersex flowers; GenetixBay treats this as a breeding fault and a reason not to breed from it.Regular seed comes from a normal cross of a female and a male, so it produces roughly half female and half male plants.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.Male selection is the choice of which male plants become parents, judged by their vigour, structure, early aroma and above all by the quality of their offspring.
