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GATE 2023 BT Q.24: solution and answer

GATE 2023 · BTQ.24 · 1 mark · MCQ

Which of the following methods are used for detection of DNA and RNA, respectively?

  1. (A)

    Southern and Northern blotting

  2. (B)

    Southern and Western blotting

  3. (C)

    Northern and Southern blotting

  4. (D)

    Northern and Western blotting

See the question in the paper
GATE 2023 BT question 24Tap to open full size

Answer and solution

ANSWER

The correct answer is (A) Southern and Northern blotting.

Official answer: ASource: Official answer key, GATE 2023 BT (IIT Kanpur)

  1. The question asks which technique detects DNA and which detects RNA, in that order (DNA first, RNA second, per "respectively").

  2. Southern blotting (named after its inventor, Edwin M. Southern) is the standard technique for detecting specific DNA sequences: DNA is digested, size-separated by gel electrophoresis, transferred to a membrane, and probed with a labeled complementary probe.

  3. Northern blotting is the analogous technique for RNA (its name is a play on "Southern"), used to detect specific RNA transcripts by size-separation, blotting, and probing.

  4. Western blotting detects proteins via antibodies, not nucleic acids, so any option pairing DNA/RNA detection with Western blotting (options B and D) is incorrect.

  5. Since the required order is DNA then RNA, the correct pairing is Southern (for DNA) and Northern (for RNA) — option (A).

  6. Option (C), "Northern and Southern," reverses the required order and is therefore incorrect.

  7. The correct choice is (A).

KEY IDEA

Southern blotting detects DNA (named after Edwin M. Southern); Northern blotting detects RNA (a naming pun on "Southern"); Western blotting detects proteins. The question asks in the order DNA, then RNA, so the pairing must be Southern, then Northern — option A.

WATCH OUT FOR

Confusing the mnemonic order — swapping Southern/Northern (option C) because the "Northern" name is a play on "Southern" and students misremember which technique targets DNA vs RNA, or wrongly pairing Western blotting (a protein-detection technique) with a nucleic acid.

From the GATE 2023 BT paper. Every question of this paper · Download the full paper · All 8 PCR & sequencing questions, with notes

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