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Given below is the restriction… (Class 12 Biology 2026, Q8)

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BiologyCBSE Class 12 · Board exam 2026, set 57/5/1 · 1 mark · MCQ

CBSE Class 12 Biology 2026: question 8

Set in the CBSE Class 12 board exam of 2026, paper 57/5/1, section A, question 8, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q8 · 1 mark · MCQBiotechnology: Principles and Processes

Given below is the restriction site of a restriction endonuclease Pst I and the cleavage sites on a DNA molecule.

5′ C — T – G – C – A ↓ G 3′
3′ G ↑ A – C – G – T — C 5′

(Top strand cleaved between A and G; bottom strand cleaved between G and A.)

Choose the option that gives the correct resultant fragments.

  1. (A)5′ C – T – G C – A – G 3′ / 3′ G – A – C – G – T C 5′
  2. (B)5′ C – T G – C – A – G 3′ / 3′ G – A – C – G T – C 5′
  3. (C)5′ C – T – G – C A – G 3′ / 3′ G – A – C – G T – C 5′
  4. (D)5′ C – T – G – C – A G 3′ / 3′ G A – C – G – T – C 5′

Figure in the paper: Two DNA strands with arrows marking cleavage sites: downward arrow on top strand between A and G, upward arrow on bottom strand between G and A. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Follow each arrow and break that strand exactly at the arrow.

Hint 2

Fragments with unequal (staggered) cuts on the two strands leave sticky ends.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. The top strand is cut between A and G, giving the fragments 5′ CTGCA and G 3′.

    ½ mark

  2. The bottom strand is cut between G and A, giving 3′ G and ACGTC 5′. The result is sticky ends, which matches option (D).

    ½ mark

Answer: (D)

Where the marks are

  • Chooses (D) (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology: Principles and Processes, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 57/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.