Feminized seeds are cannabis seeds that have been genetically engineered to produce only female plants.
Genetically, a cannabis plant is more or less predisposed to become either male or female. This is determined by two chromosomes, which are known as the X and Y chromosome. A plant with two X chromosomes becomes female. A plant with an X and a Y chromosome becomes male.
Feminized seeds are created by forcing a female plant to produce male flowers through special treatment. This essentially makes the female plant a hermaphrodite and allows it to produce seeds that have only XX or female chromosomes.
Before these seeds can actually be sold as feminized, it takes years of testing and growing to ensure that they produce plants that are absolutely stable and consistent.