The Southern blot, named for its inventor British biologist Edwin Southern, is a method for marking specific DNA sequences and detecting the presence of a specific gene. There are also Northern blots and Western blots – these blots are plays on Southern's name and have nothing to do with directions.
Blots are techniques for transferring DNA and RNA proteins onto a carrier so they can be separated, and often follows the use of a gel electrophoresis. The Southern blot is used for transferring DNA.
After electrophoresis, the gel is treated with an alkaline to cause the DNA to denature and separate into single strands. A membranous sheet is placed on the gel, and pressure applied evenly via suction or the mundane method of paper towels with a weight. The DNA migrates to the membrane and sticks there. The DNA-impregnanted membrane is baked or radiated to permanently attach the DNA. Molecules are next treated with a hybridization probe, which is simply a DNA molecule with a known sequence that will pair with the blotted DNA's sequences. The probe DNA is tagged with fluorescent or chromogenic dyes so it can be identified.
By examining the pattern of hybridization with an X-ray or autoradiography, the experimenter can determine which fragment contains specific DNA sequences or genes.
Web Resources On Southern Blot
Southern Blot Method
Book Resources On Southern Blot
Basic Techniques in Molecular Biology by Stefan Surzycki
An Introduction to Forensic DNA Analysis by Rudin & Inman