Dear student,
Cohen and Boyer performed the experiment in which they made artificial recombinant DNA molecule (rDNA). They isolated antibiotic resistance gene from a plasmid and inserted into the host plasmid of salmonella typhimurium as a vector to express the antibiotic resistance gene. As salmonella typhimurium multiplied the antibiotic resistance gene also multiplied. This was called as cloning of antibiotic resistance gene in salmonella.
Regards