Blotting techniques were developed to discriminate fragments of nucleic acids. These techniques involve several processes, including electrophoresis, which separates DNA and RNA fragments.
In Southern blotting (named after Edward Southern), restriction enzyme-cut fragments of DNA are separated by AGE or PAGE, transferred to a membrane or blot, and visualized by hybridization with labeled probes.
Northern blotting (not named after an inventor but by analogy to Southern blotting) separates RNA. RNA molecules are shorter and have defined lengths; cutting by restriction enzymes is not required. Denaturing conditions are necessary because of RNA secondary structures. After membrane blotting, the separated types of RNA are visualized with staining or labeled probes.
Western blotting (again not named after an inventor but by analogy to Southern blotting) does not separate nucleic acids; it separates proteins in a mixture. The proteins are usually separated with PAGE, transferred to the membrane, and visualized with a labeled antibody against the proteins of interest.
