If a restriction endonuclease is used on a DNA sample many times a characteristic set of fragments is obtained. If the size of these fragments is determined then these DNA sample, when digested with the same enzyme will provide a standard against which unknown DNA samples, or the same DNA sample digested with a different enzyme may be compared. In this way it is possible to estimate the size of DNA fragments of an unknown sample. The size of a DNA fragment is reported as the number of base pairs in the fragment. Two types of DNA are particularly useful for DNA research, bacterial plasmids and bacteriophages.
Plasmids are circular strands of DNA present in many bacteria.
These fragments are relatively easy to manipulate and have been extensively mapped. As such they are effective tools for genetic manipulation. A bacteriophage is a virus which infects bacteria. Once again, these phages serve as vectors and as models for DNA research. Using the HindIII digestion results as standards we will attempt to determine the approximate size of the digestion fragments from the EcoRI digest.