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Describe the steps… (Class 12 Biology SQP 2024-25, Q25)

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BiologyCBSE Class 12 · Sample paper, session 2024-25 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2024-25: question 25

From the official CBSE sample question paper for 2024-25, section C, question 25, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 3 marks · Short answerBiotechnology: Principles and Processes

Describe the steps involved in Southern blot hybridization using radiolabeled VNTR as a probe.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

This is the DNA fingerprinting procedure, done step by step.

Hint 2

DNA must first be obtained, cut and separated by size.

Hint 3

After transfer to a membrane, a labelled probe and X-ray film are used.

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. 1. Isolation of DNA from the sample cells (e.g. blood or hair root).

    ½ mark

  2. 2. Digestion of the DNA with restriction endonucleases into fragments.

    ½ mark

  3. 3. Separation of the DNA fragments by size using gel electrophoresis.

    ½ mark

  4. 4. Blotting: transfer of the separated fragments onto a synthetic membrane such as nitrocellulose or nylon.

    ½ mark

  5. 5. Hybridisation of the membrane with the radiolabelled VNTR probe, which binds to complementary sequences.

    ½ mark

  6. 6. Detection of the hybridised fragments by autoradiography, which shows a pattern of dark bands (the DNA fingerprint).

    ½ mark

Answer: Isolation of DNA → restriction digestion → gel electrophoresis → blotting on nitrocellulose/nylon → hybridisation with labelled VNTR probe → autoradiography.

Where the marks are

  • Isolation of DNA (0.5 mark)
  • Digestion by restriction endonucleases (0.5 mark)
  • Separation by electrophoresis (0.5 mark)
  • Blotting onto nitrocellulose/nylon membrane (0.5 mark)
  • Hybridisation with labelled VNTR probe (0.5 mark)
  • Detection by autoradiography (0.5 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 paperSample paper 2024-25: 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.