Correct Option
Assertion (A) states that insect-resistant transgenic cotton has been produced by inserting the Bt gene. This is factually correct. Bt cotton is a genetically modified crop that incorporates a gene from the bacterium Bacillus thuringiensis (Bt) into its genome. This gene enables the plant to produce insecticidal proteins, primarily against lepidopteran pests like bollworms, thereby conferring resistance.
Reason (R) states that the Bt gene is derived from a bacterium. This is also factually correct. The gene responsible for insect resistance in Bt cotton is indeed isolated from the soil bacterium Bacillus thuringiensis. This bacterium naturally produces crystal proteins (Cry proteins) that are toxic to specific insect larvae when ingested.
Furthermore, Reason (R) is the correct explanation for Assertion (A). The insect resistance observed in transgenic cotton (A) is directly attributed to the presence of the Bt gene, and the efficacy of this resistance stems from the fact that this gene, originating from the bacterium Bacillus thuringiensis (R), codes for insecticidal proteins. Thus, the bacterial origin of the Bt gene is fundamental to understanding how the cotton plant acquires insect resistance.
Incorrect Options
Option 2 is incorrect because Reason (R) provides a direct and accurate explanation for Assertion (A). The bacterial origin of the Bt gene is precisely why the cotton plant becomes insect resistant.
Option 3 is incorrect because Reason (R) is a true statement. The Bt gene is indeed derived from the bacterium Bacillus thuringiensis.
Option 4 is incorrect because Assertion (A) is a true statement. Insect-resistant transgenic cotton has been successfully produced using the Bt gene.