The correct answer is option ($2$) as specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton. The choice of genes depends upon the crop and the targeted pest as most Bt toxins are insect-group specific. The toxin is coded by a gene named cry. There are a number of them, for example, the proteins encoded by the genes cry $IAc$ and cry $\|Ab$ control the cotton bollworms, that of cry $IAb$ controls corn borer.