2001 General Studies, all questions

UPSC Prelims 2001 · General Studies

Question 124: Science and Technology

Assertion (A): Scientists can cut apart and paste together DNA molecules at will, regardless of the source of the molecules. Reason (R): DNA fragments can be manipulated using restriction endonucleases and DNA ligases. Which of the following is correct?

aBoth A and R are individually true and R is the correct explanation of A
bBoth A and R are individually true but R is NOT a correct explanation of A
cA is true but R is false
dA is false but R is true

AnswerThe answer is (a).

A is true in principle: with restriction enzymes and ligases, scientists can cut DNA from any source at specific sites and join the pieces, which is the basis of recombinant DNA technology. R is also true and gives the method: restriction endonucleases cut DNA at particular sequences and DNA ligases seal the pieces together. Remember restriction enzymes as molecular scissors and ligases as molecular glue.

  • A. DNA from different sources can be cut and joined.
  • R. Restriction endonucleases cut and DNA ligases join the fragments.

How you could have got this

If you were sure statement 1 is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong
  • (a) Right: both are true and R explains A.
  • (b) R is the method that makes A possible.
  • (c) R is true.
  • (d) A is true.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.