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Name and describe the steps… (Class 12 Biology 2023, Q32a)

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BiologyCBSE Class 12 · Board exam 2023, set 57/5/1 · 5 marks · Long answer

CBSE Class 12 Biology 2023: question 32(a)

Set in the CBSE Class 12 board exam of 2023, paper 57/5/1, section E, question 32(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(a) · 5 marks · Long answerBiotechnology and its Applications

Name and describe the steps involved in the technique widely used in forensics that serves as the basis of paternity testing in case of disputes.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 57/5/1.

Hints

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

Hint 1

The technique is based on repetitive DNA sequences (VNTRs) that differ between individuals.

Hint 2

Think of the order: get the DNA, cut it, separate it, blot it, probe it, see it.

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 technique is DNA fingerprinting. It compares the repetitive DNA, VNTRs (variable number of tandem repeats), of different individuals.

    1 mark

  2. Step 1 – Isolation of DNA from the sample (blood, hair root, semen, etc.).

    ½ mark

  3. Step 2 – Digestion of DNA into fragments by restriction endonucleases.

    ½ mark

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

    1 mark

  5. Step 4 – Transfer (blotting) of the separated fragments to a synthetic membrane such as nitrocellulose or nylon (Southern blotting).

    ½ mark

  6. Step 5 – Hybridisation of the fragments with a labelled (radioactive) VNTR probe.

    1 mark

  7. Step 6 – Detection of the hybridised fragments by autoradiography. This gives a band pattern unique to each person. A child's bands come half from the mother and half from the father, so comparing the patterns settles paternity.

    ½ mark

Answer: DNA fingerprinting: isolate DNA, digest it with restriction endonucleases, separate fragments by electrophoresis, blot them onto a nitrocellulose/nylon membrane, hybridise with a labelled VNTR probe, detect by autoradiography.

Where the marks are

  • Names DNA fingerprinting (1 mark)
  • Isolation of DNA (½ mark)
  • Digestion by restriction endonuclease (½ mark)
  • Separation of fragments by electrophoresis (½ × 2 = 1 mark)
  • Transfer to a nitrocellulose or nylon membrane (½ mark)
  • Hybridisation using a labelled VNTR probe (½ × 2 = 1 mark)
  • Detection by autoradiography (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology and its Applications, one at a time, marked against the answer key and marking points.Back to the full paper2023 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.