What is Cas9 protein that is often mentioned in news?
- (a) A molecular scissors used in targeted gene editing ✓ UPSC's answer
- (b) A biosensor used in the accurate detection of pathogens in patients
- (c) A gene that makes plants pest-resistant
- (d) A herbicidal substance synthesized in genetically modified crops
Why the answer is (a)
• Cas9 (CRISPR-associated protein 9) is an enzyme that, guided by a short RNA, cuts DNA at a precise target sequence — the 'molecular scissors' of CRISPR-Cas9 gene editing — option (a).
• Derived from a bacterial immune system, it lets scientists delete, repair or insert genes; Doudna and Charpentier won the 2020 Nobel Prize in Chemistry for it.
• It is not a biosensor (b) — though CRISPR-based diagnostics exist — nor a pest-resistance gene (c) or a herbicide (d).
• Hence option (a).
Why the other options are wrong
- (b) A biosensor used in the accurate detection of pathogens in patients
- Cas9 is an enzyme for cutting DNA, not a biosensor.
- (c) A gene that makes plants pest-resistant
- Cas9 is a protein, not a plant resistance gene.
- (d) A herbicidal substance synthesized in genetically modified crops
- Cas9 is not a herbicide.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2019, held on 2 June 2019. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.