Since the discovery of structure of DNA by Watson and Crick, electrophoresis has been
established as the most commonly used approach to analyze size, shape, and structure of
DNA molecules. DNA molecules vary greatly in size, from a few nucleotides one can easily
synthesize in vitro to long chains of millions of base pairs such as eukaryotic chromosomes.
DNA comes in a variety of forms: it can be single stranded or double stranded,
linear or circular, or supercoiled or relaxed; it can be bound, bent, or modifi ed by proteins;
it forms sophisticated branched structures during replication and recombination. DNA
electrophoresis is a powerful tool that allows separating DNA molecules according to their
size and shape.