CASE STUDY
Some strains of Bacillus thuringiensis produce protein that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. The Bt toxin proteins exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form due to alkaline pH of the gut which solubilise the crystals.
The proteins encoded by the genes cryIAc and cryIIAb control :
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Cotton bollworms
The Bt toxin is coded by cry genes. Most Bt toxins work on one group of insects, so the gene is chosen to suit the crop and its pest.
Option (1) Corn borers — Incorrect. The corn borer is controlled by the protein of cryIAb.
Option (2) Cotton bollworms — Correct. The proteins of cryIAc and cryIIAb control the cotton bollworms, as in Bt cotton.
Option (3) Mosquitoes — Incorrect. Some Bt strains kill dipterans such as mosquitoes, but not through these two genes.
Option (4) Nematodes — Incorrect. Nematodes are not insects. They are controlled by RNA interference, not by cry genes.
Note 1: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
Note 2: A similar question was also asked in CUET (UG) 2026 on 19-05-2026 (Slot 1).
NCERT Extract:
Biotechnological Applications in Agriculture – “… Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton (Figure 10.1). 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.”