Plasmid is a small, circular and double-stranded DNA molecule which is different from the cell's chromosomal DNA, and they naturally exist in bacterial cells. Plasmids carry genes which provide bacteria with genetic advantage such as antibiotic resistance. Researchers can insert DNA fragments or genes into the plasmid vector creating a recombinant plasmid. The recombinant plasmid is then inserted into the bacterium by a process called transformation. Then since bacteria divide rapidly, they can be used as factories to copy DNA fragments in large quantities