Southern blotting

This representation shows the steps in Southern blotting.
Step 1: Genomic DNA is digested by a restriction enzyme.
Step 2: DNA is run on an agarose gel, giving a smeared appearance.
Step 3: DNA is transferred from the gel to a membrane.
Step 4: A radioactive probe is hybridized to the membrane and the membrane is exposed to X-ray film. The bands show the places where the probe hybridized to the patient DNA. If the DNA has a gene deletion or a mutation that eliminates a restriction enzyme site, then one or more bands may be missing. This step can also be performed using a non-radioactive probe.
In the final image, normal individuals (Lanes 2 to 4) show the expected pattern, while an individual with a partial gene deletion (Lane 5) is missing one of the bands.