Conjugation is the major route for genetic exchange between different phylogenic groups of prokaryote cells and between prokaryotes and eukaryotes. The transfer machinery involved is usually encoded by plasmids or conjugative transposons. Transformation was the first gene transfer mechanism to be discovered. The donor in conjugative transfer is a bacterium that contains a conjugative plasmid or conjugative transposon, which mediates DNA transfer to a recipient. A genetic element that can exist either as an autonomous genetic element or that is integrated into the host's chromosome.
Some plasmids are episomes.