Bt cotton is a genetically modified plant contain a gene (Cry IAc, Cry IIAb) cry genes of Bacillus thuringiensis (Bt). Which control lepidopteran insects by producing toxin protein. Normal cotton plant do not consists such genes. These cry gqnes which produced toxic protein crystals produce different strains of toxins. That cry gene isolated from bacteria and inserted into cotton plant DNA through rDNA technology where bacterial gene get cloned inside the cotton plant to produced large quantity of pro - toxic in plant cell. Specific cry gene are inserted to produce resistancy for particular insects according to the region of world.