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Explain the basis on which… (Class 12 Biology 2025, Q27)

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BiologyCBSE Class 12 · Board exam 2025, set 57/1/1 · 3 marks · Short answer

CBSE Class 12 Biology 2025: question 27

Set in the CBSE Class 12 board exam of 2025, paper 57/1/1, section C, question 27, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q27 · 3 marks · Short answerBiotechnology: Principles and Processes

Explain the basis on which gel electrophoresis technique works. Write any two ways the products obtained through this technique can be utilised.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/1/1.

Hints

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

Hint 1

What charge does DNA carry because of its phosphate groups?

Hint 2

How does the gel matrix affect fragments of different lengths?

Hint 3

Once separated, why would scientists want a pure DNA fragment?

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. Basis (1): DNA is negatively charged. In an electric field, DNA fragments therefore move through the matrix (agarose gel) towards the anode.

    1 mark

  2. Basis (2): The agarose gel acts as a sieve. Fragments separate according to their size: smaller fragments move faster and farther. The separated bands are seen after staining with ethidium bromide under UV light, and are then cut out and eluted.

    1 mark

  3. Uses of the eluted fragments (any two):

    • constructing recombinant DNA by joining them with cloning vectors
    • DNA fingerprinting
    • amplification by PCR
    1 mark

Answer: Negatively charged DNA moves towards the anode and is separated by size through the sieving gel (smaller fragments move faster); the fragments are used in rDNA technology, DNA fingerprinting and PCR.

Where the marks are

  • DNA is negatively charged and moves towards the anode in an electric field through a matrix (1 mark)
  • Separation by size through the sieving effect; smaller fragments move faster (1 mark)
  • Any two uses, e.g. rDNA technology, DNA fingerprinting, PCR (½ + ½ marks)

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 paper2025 board paper, set 57/1/1: 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.