Southern blotting is used to detect specific DNA sequences. The correct sequence of steps is:

• A RNA extraction → gel electrophoresis → transfer to membrane → hybridisation with labelled probe (Northern blotting steps)
• B DNA restriction digest → agarose gel electrophoresis → denaturation → transfer to nitrocellulose membrane → hybridisation with labelled probe → detection ✓
• C Protein SDS-PAGE → transfer to PVDF membrane → blocking → primary antibody → secondary antibody (Western blotting steps)
• D DNA PCR → cloning into vector → colony blotting → hybridisation

Explanation

Southern blotting (named after Ed Southern) involves: restriction enzyme digestion of genomic DNA → agarose gel electrophoresis by size → in-situ alkaline denaturation to single-stranded DNA → capillary or vacuum transfer to nylon/nitrocellulose membrane → UV crosslinking → hybridisation with a specific labelled (radioactive or chemiluminescent) probe → autoradiography/imaging. It detects specific DNA sequences and restriction fragment length polymorphisms (RFLPs). Northern = RNA; Western = protein.

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

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