Gel electrophoresis (Gel electrophoresis) refers to the technique of electrophoresis that is needed to detect the quantity and quality of DNA molecules after they have been extracted. Agarose or polyacrylamide gel electrophoresis is one of the core techniques of genetic manipulation, which can be used to isolate, identify and purify DNA fragments. The technique is simple and rapid to perform and has become a versatile method for many molecular biology studies, such as DNA recombination and DNA nucleotide sequence analysis.

When a molecule is placed in an electric field, it moves to the appropriate electrode at a certain speed, and the speed of migration of electrophoretic molecules under the action of an electric field is called the mobility of electrophoresis. It is proportional to the strength of the electric field and the net charge carried by the electrophoretic molecules themselves. That is to say, the greater the strength of the electric field and the greater the number of net charges carried by the electrophoretic molecules, the faster their migration speed will be, and vice versa will be slower. The migration rate of electrophoresis is again inversely proportional to the coefficient of friction of the molecules due to the use of an unreactive and stable support medium in electrophoresis, such as agarose gels and polyacrylamide gels, which reduces the convective motion. The coefficient of friction is known to be a function of molecular size, polarity, and viscosity of the medium, so that various components of a mixture of protein or nucleic acid molecules can be separated from each other by electrophoresis based on differences in molecular size, composition, or shape, as well as the amount of net charge they carry. Under physiological conditions, the phosphate groups in the sugar-phosphate backbone of a nucleic acid molecule are in an ionic state, and in this sense, DNA and RNA polynucleotide chains may be called polyanions. Therefore, when nucleic acid molecules are placed in an electric field, they migrate in the direction of the positive electrode. Due to the repetitive nature in the structure of the sugar-phosphate backbone, the same number of double-stranded DNAs have almost equal net charges, and thus they can migrate at the same rate in the direction of the positive electrode. Under a certain electric field strength, this migration speed of DNA molecules, i.e., the electrophoretic mobility, depends on the size and configuration of the nucleic acid molecules themselves, and DNA molecules with smaller molecular weights migrate faster than DNA molecules with larger molecular weights. This is the basic principle of applying gel electrophoresis to separate DNA fragments.