ABSTRACT
Digestion of a purified chromosomal DNA sample with restriction enzymes overcomes the problem of the heterogeneous mixture of DNA fragments normally present in a chromosomal DNA sample. When the randomly sized chromosomal DNA fragments are completely digested with a restriction enzyme, the DNA will be cleaved at all of the recognition sites for that enzyme. Digestion of randomly sized chromosomal DNA with a restriction enzyme generates specific sets of DNA fragments that are defined at their ends by the restriction cleavage sites. Following digestion of a DNA molecule with restriction enzymes, the size classes of DNA fragments must be separated from one another so that the DNA fragments can be visualized and the sizes of the fragments determined. When a sample of chromosomal DNA that has been digested with a restriction enzyme is loaded in the sample well of an agarose gel and electric current applied to the gel, the DNA fragments migrate into the gel and separate by size.
