Correct Option (B)
Insect-resistant cotton plants, specifically Bt cotton, are genetically engineered by incorporating a gene from the bacterium Bacillus thuringiensis (Bt). This bacterium naturally produces proteins that are toxic to certain insect pests, particularly lepidopteran larvae like the cotton bollworm. The gene encoding these insecticidal proteins (Cry proteins) is isolated from Bacillus thuringiensis and introduced into the cotton plant's genome, enabling the plant to produce its own insecticidal toxins and thus confer resistance against these pests.
Incorrect Options:
(A) Virus: While viruses are used in genetic engineering as vectors to deliver genes, the specific gene conferring insect resistance in Bt cotton originates from a bacterium, not a virus. Viral genes are not directly responsible for the insecticidal properties in this context.
(C) Insect: Genes from insects are not used to create insect-resistant cotton. The mechanism of resistance in Bt cotton involves the production of toxins that target insects, not the incorporation of insect genetic material into the plant.
(D) Plant: While genetic engineering can involve transferring genes between different plant species, the insect-resistant trait in Bt cotton is derived from a non-plant organism, specifically a bacterium. Genes from other plants are not the source of resistance in this particular genetically modified crop.