Agarose gel electrophoresis.

Agarose gel electrophoresis is used to resolve DNA fragments on the basis of their molecular weight. Smaller fragments migrate faster than the larger ones; the distance migrated on the gel varies inversely with the logarithm of the molecular weight. The size of fragments is determined by calibrating the gel, using known size standards, and comparing the distance that the unknown fragment has migrated. In the method described in the chapter, this technique is used to resolve complex DNAs for Southern blot analysis or to resolve simpler digests of bacteriophage and plasmid clones for RE site mapping and blotting. The time required to carry out this procedure is two days. . Reagents such as agarose, ethidium bromide, and gel loading buffer are required. DNA is prepared and analyzed in advance including RE digest.