In 1974, the modern era of biotechnology began when Stanley Cohen of Stanford University and Herbert Boyer of the University of California at San Francisco successfully recombined ends of bacterial DNA after splicing a toad gene in between. They called their accomplishment recombinant DNA, but the media preferred the term genetic engineering.

Boyer and Cohen’s achievement was an advancement upon the techniques developed by Paul Berg, in 1972, for inserting viral DNA into bacterial DNA. Cohen’s research at Stanford was with plasmidsﾗthe nonchromosomal, circular units of DNA found in, and exchanged by, bacteria, while Boyer’s was restriction enzymes produced by bacteria to counter invasion by bacteriophages.