In RNAi genes are silenced by :

The correct answer is Option (3) → ds RNA

Option (1) ss RNA — Incorrect. The target mRNA is single-stranded; the silencing molecule is double-stranded.

Option (2) ss DNA — Incorrect. RNAi silences an mRNA with a complementary RNA, not DNA. Single-stranded DNA plays no part; the silencing molecule is double-stranded RNA.

Option (3) ds RNA — Correct. In RNA interference, a complementary dsRNA binds to a specific mRNA and prevents its translation, silencing the gene. The dsRNA may come from an infecting RNA virus or from transposons.

Option (4) ds DNA — Incorrect. Double-stranded DNA is the genome itself; it does not silence mRNA.

Note: A similar question was also asked in CUET (UG) 2025 on 23-05-2025 (Slot 2), and in CUET (UG) 2023 on 12-06-2023 (Slot 2).

NCERT Extract:
Biotechnological Applications in Agriculture – “… Pest Resistant Plants: Several nematodes parasitise a wide variety of plants and animals including human beings. A nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (RNAi). RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing).”