Explanation
- A
A molecular scissors used in targeted gene editing
(a) Cas9 is a molecular scissors: an RNA-guided endonuclease from CRISPR systems that cuts DNA at a targeted site so that gene editing (NHEJ or HDR) can follow. That is the official key.
- B
A biosensor used in the accurate detection of pathogens in patients
(b) A biosensor for pathogens is a different class of device (antigen tests, CRISPR diagnostics exist, but Cas9-as-such is not “a biosensor”). Not the key.
- C
A gene that makes plants pest-resistant
(c) Pest-resistance genes (Bt cry genes, for example) are not Cas9. Cas9 is the cutting enzyme, not a plant trait gene. Not the key.
- D
A herbicidal substance synthesized in genetically
(d) A herbicidal substance made in a genetically modified plant is not Cas9. Not the key.
Summary. Official key is (a). Cas9 is the CRISPR-associated nuclease that cuts targeted DNA. It is not a pathogen biosensor, not a pest-resistance gene, and not a herbicide. Honour (a).
Same topic · past papers
UPSC has asked this before
These previous-year questions sit on the same topic. Open one to practise the earlier ask.
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Consider the following statements: 1. Light is affected by gravity. 2. The Universe is constantly expanding. 3. Matter warps its surrounding space-time. Which of the above is/are the prediction/predictions of Albert Einstein's General Theory of Relativity, often discussed in media? -
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