refers to a number of similar techniques that facilitate the analysis of biological molecules. Initially, mixtures of proteins or dna or rna fragments are separated by electrophoresis through a polymeric gel (most commonly agarose or polyacrylamide). The separated components are then transferred to a membrane where they are immobilised and can be analysed and visualised by a variety of techniques, including antibody binding and dna hyrbridisation. Some of the various types of blots are briefly described below. Southern blot - The gel is a dna electrophoresis system and the molecules transferred are dna molecules. Northern blot - similar to the southern blot, but used to analyse rna. Western blot - The molecules analysed in a western blot are proteins, separated by gel electrophoresis, then identified by reacting them with an antibody. Southwestern blot - this is a variant of the southern blot used to find protein molecules that stick to dna molecules. Dot blot. Dna, rna, or protein are dotted directly onto the membrane support, so that they form discrete spots.