The method is named after its inventor, the British biologist Edwin Southern. Southern blotting is a hybridization technique that enables researchers to determine the presence of certain nucleotide sequences in a sample of DNA. This technique involves the following steps:
DNA is digested with one or more restriction enzymes, and the resulting fragments are separated according to size by electrophoresis through agarose or polyacrylamide gel.
The DNA is denatured and transferred from the gel to a solid support, i.e. nitrocellulose membrane by a technique called blotting.
The reason for transferring the DNA fragments to a solid support (usually a nitrocellulose plate) is that the DNA is inaccessible to DNA probes while embedded in the gel.
The relative positions of the DNA fragments are preserved during their transfer to the filter. The DNA fragments attached to the filter are then exposed to a strand of radioactively labelled DNA that is complementary to the DNA strand on the plate that is of interest.
Autoradiography is then used to locate the positions of bands complementary to the probe.