Question

Cry II Ab and cry I Ab produce toxins that control
(A) Cotton bollworms and corn borer respectively.
(B) Corn borer and cotton bollworms respectively.
(C) Tobacco budworms and nematodes respectively.
(D) Nematodes and tobacco budworms respectively.
(E) Corn borer and tobacco budworms respectively.

Answer 1

Cry gene such as Cry II Ab and Cry I Ab encodes for Cry protein. Cry protein stands for crystal protein which is obtained from a bacteria known as Bacillus thuringiensis. These proteins are isolated in order to be transferred into many crops.

Complete answer:
A crop consisting of the cry gene shows resistance towards a group of Insects.
Cry protein is toxic in certain groups of insects. The toxicity is observed in the larvae of such insects.
The proteins which are encoded by cry II Ab control the cotton bollworms
The cry I Ab encodes a protein which controls corn borer
Cotton bollworms are also controlled by proteins that are encoded by cry I Ac.
Examples of insects that are affected by cry genes are lepidopterans (tobacco budworm, armyworm), coleopterans i.e. beetles, and dipterans like flies, mosquitoes, etc.

Therefore the correct option is (A) Cotton bollworms and corn borer respectively.

Note:
Bacillus thuringiensis forms toxic insecticidal protein crystals during a particular phase of their growth. These toxic proteins are produced in an inactive form which becomes active after ingestion by the insects. The inactive form of this toxin protein gets converted into the toxic form due to the alkaline PH of the gut. Alkaline PH solubilizes the crystals. The activated toxin then binds to the surface of the midgut epithelial cells and causes the swelling of the cells along with cell lysis which eventually causes the death of the insect. An example of a transgenic crop consisting of cry genes is BT cotton. BT cotton provides pest resistance and high yield.