Southern blotting detects specific DNA sequences. The correct order of steps is:

• A Restriction digestion → gel electrophoresis → transfer to nylon membrane → hybridisation with labelled RNA probe → autoradiography
• B Restriction digestion → gel electrophoresis → transfer to nylon membrane → hybridisation with labelled DNA/RNA probe → detection ✓
• C PCR amplification → gel electrophoresis → transfer → hybridisation → detection
• D mRNA isolation → reverse transcription → gel electrophoresis → hybridisation → detection

Explanation

Southern blotting: genomic DNA → restriction enzyme digestion → agarose gel electrophoresis → denaturation → capillary/vacuum transfer to nylon membrane → hybridisation with labelled probe (DNA or RNA) → washing and autoradiography/fluorescence detection. PCR amplification before electrophoresis is not part of classic Southern blot. mRNA isolation and reverse transcription describe Northern blotting (RNA detection) or RT-PCR.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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