Which of the following statements about Bt toxins and cry genes are correct?
A. Bacillus thuringiensis forms protein crystals during a particular phase of its growth.
B. The protein encoded by the gene cryIAb controls corn borer.
C. The proteins encoded by the genes cryIAc and cryIIAb control corn borer.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A and B only
A. Bacillus thuringiensis forms protein crystals during a particular phase of its growth. — True. These crystals contain a toxic insecticidal protein that stays inactive (protoxin) inside the bacterium. It becomes active only in the alkaline gut of the insect.
B. The protein encoded by the gene cryIAb controls corn borer. — True. The cry genes are chosen by crop and pest, because most Bt toxins are insect-group specific. The cryIAb protein controls corn borer.
C. The proteins encoded by the genes cryIAc and cryIIAb control corn borer. — False. The proteins of cryIAc and cryIIAb control the cotton bollworms, which is why these genes are used in Bt cotton. The statement puts corn borer in place of cotton bollworms.
NCERT Extract:
Biotechnological Applications in Agriculture – “… B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.”
Biotechnological Applications in Agriculture – “… 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 cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer.”