ABSTRACT
The discovery of restriction enzymes that cleave DNA in a site-specific manner to generate discrete gene fragments might be considered the first crucial element in the development of the ability to make novel recombinant DNA molecules in vitro, or in a test tube. Shortly after the discovery that restriction enzymes can be used to cleave DNA into fragments with specific, defined ends, researchers realized that the short, cohesive termini generated by many restriction enzymes could be used to make new combinations of DNA fragments recombinant DNA molecules. This process allows the recombination of DNA fragments that are similar only in the presence of a restriction enzyme cleavage site. However, in the test tube, restriction enzymes can be used to cleave the two unrelated DNA molecules to generate short, cohesive single-stranded ends and the ends allowed to anneal to generate new combinations of DNA fragments.
