This is all you a bit of what you should have in mind
Originally posted on Marijuana & Cannabis Blog:
Cannabis plants are either male or female. The male plants produce pollen which pollinates the flowers of the female plant, which once pollinated, produce seeds. If the female plant is not pollinated (if there are no male plants nearby producing pollen), the flower/buds continue to develop and produce THC. Female plants which are not pollinated are referred to as sensemilla (without seeds).
Usually 40-50% of the plants are male.
A female can either generate a large seedless bud, a large bud with a few seeds, or a large bud that is almost totally seeds. The first case is achieved by removing all the male plants before any of their flowers open. The second case occurs when a few male flowers have opened but you remove them before any more open. The third case occurs when you miss-time the flowering of the male. This can be devastating if you have big female plants because you could loose 90% of the smokable herb to seed production.