Because bacteria reproduce asexually and therefore produce clonal copies, novel genetic variation must be acquired laterally, and genetic recombination in bacteria proceeds by three distinct mechanisms defined by the vehicle of DNA transfer: transformation, the uptake of free ("naked") DNA from the environment through transient membrane permeability; conjugation, the direct transfer of a replicated plasmid from a fertility-factor-bearing donor (F+) to a recipient (F−) through a hollow protein bridge called the sex pilus; and transduction, the transfer of bacterial plasmid or chromosomal DNA between hosts by a bacteriophage that mispackages host sequence during viral repackaging. Plasmids — extrachromosomal circular DNA elements — are the principal mobile units in transformation and conjugation, and the framework belongs to microbiology and bacterial genetics, explaining how traits such as antibiotic resistance spread through populations independently of vertical descent.
Because bacteria reproduce asexually and therefore produce clonal copies, novel genetic variation must be acquired laterally, and genetic recombination in bacteria proceeds by three distinct mechanis…