The technique was invented in mid-1970s by Edward Southern. Animation of Southern Blotting - From Cold Spring Harbor Lab. The DNA fragments in the gel are denatured with alkaline solution and transferred onto a nitrocellulose filter or nylon membrane by blotting, preserving the distribution of the DNA fragments in the gel. The nitrocellulose filter is incubated with a specific probe. The location of the DNA fragment that hybridizes with the probe can be displayed by autoradiography.
Polymorphism refers to the DNA sequence variation between individuals of a species.
The most well known example is the RFLP due to b globin gene mutation. Thus, Mst II will generate 0.2 kb and 1.2 kb fragments in the normal cell, but generate 1.4 kb fragment in the sickle cell. These different fragments can be detected by southern blotting. In the Southern blotting, DNA fragments are denatured with alkaline solution. In the Northern blotting, RNA fragments are treated with formaldehyde to ensure linear conformation.