Biotechnology and It's Applications — NEET UG practice

Background: specific Bt toxin genes were isolated from Bacillus thuringiensis and inserted into crop plants such as cotton and corn to make them pest-resistant.

Since most Bt toxins are insect-group specific, the choice of gene depends on which pest the crop needs protection from.

The gene cryIAc codes for a toxin protein that specifically controls cotton bollworms.

The gene cryIAb codes for a toxin protein that specifically controls the corn borer.

Matching this order (cotton bollworm, then corn borer) to the options, we get cryIAc and cryIAb respectively.

Hence, the correct answer is A: cryIAc and cryIAb.

Background: Bacillus thuringiensis (Bt) makes crystal proteins that are stored inside the bacterium as inactive protoxins — they cannot harm any insect in this form.

Since the protoxin is harmless until it changes shape, we need to find out what triggers this change once the insect swallows it.

The insect gut has an alkaline pH, and this alkaline environment solubilises the toxin crystals, which converts the inactive protoxin into the active toxin form.

This activated toxin then binds to the midgut cells and creates pores, eventually killing the insect — but that activation step itself depends only on pH, not on enzymes like nucleases or proteases.

Hence, the correct answer is B: due to alkaline pH.

Transgenic animals: these are animals whose DNA has been modified to include a foreign gene, so that they can be used as living factories to produce useful human proteins.

α-1-antitrypsin is one such human protein that can be obtained from transgenic animals; in humans it normally protects lung tissue by inhibiting enzymes that would otherwise damage it.

When this protein is deficient or missing, lung tissue gets damaged, leading to the disease called emphysema. So supplying α-1-antitrypsin from transgenic sources is used to treat emphysema.

The other options — Alzheimer's disease, rheumatoid arthritis, and cystic fibrosis — are diseases for which transgenic animal models exist to study the disease, but they are not treated using α-1-antitrypsin.

Hence, the correct answer is A: Emphysema.