Electrophoresis

Highly purified agarose, a major component of seaweed, is used as the solid gel matrix into which the DNA Figure 2. Illustration by Hans & Cassidy. Courtesy of Gale Group. samples are loaded for electrophoresis. By varying the agarose concentration in the gel, DNA fragments in different size ranges can be separated.

The agarose is dissolved in water, heated and cast as a gel slab approximately 0.2 in (0.5 cm) in thickness. Wells are formed at one end of the gel for the loading of the DNA sample. The slab is then placed horizontally into the electrophoresis buffer chamber (Figure 2).

The DNA migrates in bands toward the positive electrode. The smaller molecules pass through the matrix more rapidly than the larger ones, which are restricted. The DNA bands are then stained using a fluorescent dye such as ethidium bromide. The stained gel is then viewed directly under ultraviolet light and photographed.