Question

Consider the following statements Assertion (A): The RNAi can be introduced in an organism by insertion of gene encoding ssRNA only. Reason (R): RNAi takes place in all eukaryotic organisms as a method of cellular defence.

• A. Both (A) and (R) are true, (R) is the correct explanation of (A)
• B. Both (A) and (R) are true, (R) is not the correct explanation of (A)
• C. (A) is true, but (R) is false
• D. (A) is false, but (R) is true

Hint:

RNA interference is triggered by double-stranded RNA (dsRNA), which is processed into siRNA molecules that degrade complementary mRNA and block gene expression.

Answer 1

The Correct Option is D

Concept: RNA interference (RNAi) is a cellular mechanism in which a specific messenger RNA (mRNA) is silenced or degraded, thereby preventing the synthesis of a particular protein. This phenomenon was first observed in plants and later found to be widespread among eukaryotic organisms. The process is triggered by double-stranded RNA (dsRNA), not merely by single-stranded RNA (ssRNA). The dsRNA is recognized by cellular machinery and is processed into small interfering RNAs (siRNAs), which guide the degradation of complementary mRNA molecules.

Step 1: Examine the Assertion. The assertion states that RNAi can be introduced by inserting a gene encoding only single-stranded RNA. This statement is incorrect. For RNA interference to occur effectively, the inserted gene must produce RNA capable of forming double-stranded RNA molecules. In many transgenic organisms, a gene is inserted in such a way that both sense and antisense RNAs are produced, which pair together to form dsRNA. Since dsRNA is the actual trigger for RNAi, the assertion is false.

Step 2: Examine the Reason. The reason states that RNAi occurs in all eukaryotic organisms as a method of cellular defence. This statement is correct. RNAi acts as a natural defence mechanism against:
• Viruses
• Transposons
• Foreign genetic elements By degrading foreign RNA molecules, RNAi protects the cell from harmful genetic invaders.

Step 3: Determine the correct option. The assertion is false because RNAi requires dsRNA rather than only ssRNA. The reason is true because RNAi functions as a cellular defence mechanism in eukaryotes. Therefore, the correct answer is option (D).