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. Transposons also carry other genes, often those encoding antibiotic resistance. Transposable elements can be used as biological mutagens. Although still important tools, they have largely been supplanted by restriction enzyme analysis, cloning, and DNA sequencing for study of bacterial genomes.