Question

Insect pest resistant Bt-cotton plant was developed using
a. Somaclonal variation
b. Micropropagation
c. Somatic hybridization
d. Transgenic technology

Answer 1

Hint: Plant tissue culture produces variations in plants in a method referred to as somaclonal variation. The production of progeny plants via rapid multiplication of the stock plant is known as micropropagation. Protoplast fusion helps in the manipulation of cellular genomes via somatic hybridization. The introduction of foreign genes via genetic engineering is referred to as transgenic technology.

Complete answer:
In short for a bacterium called Bacillus thuringiensis.
• Some strains of this Bt produce proteins that kill insects. These are present as crystal proteins. These crystals contain a toxic insecticidal protein.
• Since the Bt toxin protein exists as inactive proteins, it cannot kill the bacterium.
• Once an insect digests this protoxin, it is converted into an active form due to the alkaline nature of the gut.
• The binding of the toxin causes cell swelling and eventually death of the insect.
• Hence, specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into cotton plants.
• A gene named cry encodes the toxin.

Hence, the correct answer is option (D).

Additional information:
• The choice of the gene is dependent on the crop into which it is incorporated and the targeted pest.
• The proteins encoded by the genes control the cotton bollworms are controlled by the proteins encoded by the genes cryIAc and cryIIAb. The corn borer is controlled by the gene cryIAb.

Note: Some important points to remember:
• Bt toxins are insect-group specific.
• Insects like lepidopterans, coleopterans, and dipterans are examples of insects that are killed by Bt toxins.
• There are two techniques for foreign gene(transgene) introduction into the plant cell genome. One is through a vector. The second method is through the direct introduction of DNA.