Plasmids as Genetic Tools and Their Applications in Ecology and Evolution

Plasmids are genetic elements of DNA molecules in the form of small circles present within the bacterial cell cytoplasm outside the bacterial chromosome. Because they are separate from the chromosome, they reproduce independently. However, plasmids are bound to multiply in the cell by multiplying the chromosome. Plasmids differ in size and number of copies in the cell. Plasmids carry genes that add to the cell additional properties, but they are not necessary for cell life and do not affect cell vitality. Some chemicals can remove plasmids from the cell by stopping their proliferation. By bacterial cell multiplication, the number of plasmids decreases until bacterial cells free from the plasmids are obtained. Plasmids are used in the techniques and research of genetic engineering and gene therapy by gene transfer to bacterial cells or to cells of superior organisms, whether other plants, animals, or other living organisms, to improve their resistance to diseases or to improve their growth rates or to improve any other required traits