plasmid

Small, mobile piece of DNA found in bacteria that, for example, confers antibiotic resistance, used in genetic engineering. Plasmids are separate from the bacterial chromosome but still multiply during cell growth. Their size ranges from 3% to 20% of the size of the chromosome. Some plasmids carry ‘fertility genes’ that enable them to move from one bacterium to another and transfer genetic information between strains. Plasmid genes determine a wide variety of bacterial properties including resistance to antibiotics and the ability to produce toxins.