In specialized transduction, the donor DNA can replicate inside the recipient cell without homologous recombination taking place, but this is not true in generalized transduction. The genetic information that plasmids carry is not essential for cell function under all conditions, but may confer selective growth advantage under certain conditions. Examples include, antibiotic resistance, enzymes for degradation of unusual organic compounds, and special metabolic pathways. Closely related plasmids cannot both replicate in the same cell. Some plasmids can transfer from cell to cell by a mechanism called conjugation.
Conjugative plasmids tend to be large.
However, other genetic elements, including the donor cell chromosome, can sometimes be mobilized, and also transferred. Transfer of the host chromosome is rarely complete, but can be used to map the order of the genes on the chromosome. Transposition can be either replicative or conservative. Two types of transposable elements are insertion sequences and transposons. Both have inverted repeats at their ends, and both encode a transposase, an enzyme involved in transposition.