‘RNA interference (RNAi)’ technology has gained popularity in the last few years. Why? I. It is used in developing gene silencing therapies. II. It can be used in developing therapies for the treatment of cancer. III. It can be used to develop hormone replacement therapies. IV. It can be used to produce crop plants that are resistant to viral pathogens. Select the correct answer using the codes given below:

The correct answer is A. Statements I, II and IV are valid; statement III is not.

RNA interference is a natural cellular mechanism in which small RNA molecules such as siRNA and miRNA guide the degradation or blocking of specific messenger RNA, so the gene is silenced without changing the DNA. That is why it is called gene silencing.

• Statement I is correct. Gene silencing therapies are the core application, and siRNA-based drugs have been approved for conditions such as hereditary transthyretin amyloidosis.
• Statement II is correct. RNAi is being tested to silence oncogenes and genes that help tumours survive and resist drugs.
• Statement III is wrong. Hormone replacement needs the hormone itself or an analogue. RNAi reduces gene expression and cannot supply a missing hormone.
• Statement IV is correct. Plants engineered to produce double-stranded RNA against viral genes, such as virus-resistant papaya, show RNAi-based viral resistance.

Mains angle: biotechnology and bioethics in GS-III, including regulation of genetically modified crops and the cost and access of gene-based drugs.

Trap: Many aspirants pick B or C because they assume every biotech buzzword has a medical use, or they confuse gene silencing with gene replacement.