Southern blotting is a laboratory technique used to detect a specific DNA sequence in a blood or tissue sample. A restriction enzyme is used to cut a sample of DNA into fragments that are separated using gel electrophoresis. The DNA fragments are transferred out of the gel to the surface of a membrane. The membrane is exposed to a DNA probe labeled with a radioactive or chemical tag. If the probe binds to the membrane, then the probe sequence is present in the sample.
A Southern blot is a way to analyze DNA molecules. The protocol was developed by Edward Southern. And if you were going to perform a Southern blot, you would first want to separate DNA based upon size in a gel along an electric field... And so your larger fragments, again, at the top; your smaller fragments are going to be at the bottom. When you're done running your gel, you then transfer that to a membrane. So it's like making a sandwich: gel, membrane on top, stack of paper towels. And what you're looking for is, you're going to allow a solution to pass through the gel, up to the membrane, and it's going to be a soft gradient that pushes it through.Stacie Loftus, Ph.D.