How does Southern Blot work?

1. DNA fragments separated by size using gel electrophoresis
2. Gel slab containing DNA fragments laid under nitrocellulose membrane, set in alkaline medium to denature dsDNA into ssDNA. ssDNA is drawn upwards onto the nitrocellulose membrane and binds to the membrane.
3. Membrane incubated with probe complementary to the target sequence in the DNA fragments, which contains radioactive marker. Hybridization via complementary base pairing occurs.
4. The bands formed are then visualized using autoradiography. Radioactive regions expose the film, forming image that shows where the bands have formed complementary base pairs with the probe.