Procedure of Southern blotting
1. Allow DNA sample to be cut by restriction enzymes
2. Fragments of sample separated via gel electrophoresis
3. Gel slab with fragments placed between nitrocellulose membrane and paper towels (top) and absorbent sponge in alkaline solution (bottom)
4. Paper towels draw alkaline solution up through the gel, denatures and separates double-stranded DNA fragments, single-stranded DNA fragments drawn upwards onto nitrocellulose membrane (binds in same position as gel)
5. Membrane is incubated with radioactive single-stranded DNA probe (probe consists of single-stranded DNA synthesised to be complementary to part of target sequence, only DNA fragments with target sequence will hybridise to probe)
6. Membrane washed to remove unhybridised probes
7. Autoradiography (x-ray film over membrane), radioactivity of bound probes exposes film to form image corresponding to bands base-paired to probe