UPSC Prelims 2019 GS Paper I · Q99 of 100 General Science easy

What is Cas9 protein that is often mentioned in news?

  1. (a) A molecular scissors used in targeted gene editing ✓ UPSC's answer
  2. (b) A biosensor used in the accurate detection of pathogens in patients
  3. (c) A gene that makes plants pest-resistant
  4. (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.

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