In a process called conjugation, genetic material is transferred
between two bacterial cells (of the same or different
species) that are temporarily joined. The DNA transfer is one~
way: One cell donates the DNA, and the other receives it. The
donor uses sex pili to attach to the recipient (Figure 27.12).
After contacting a recipient cell, each sex pilus retracts, pulling
the two cells together, much like a grappling hook. Atempo·
rary"mating bridgeH then forms bern'een the two cells, provid·
ing an avenue for DNA transfer.
In most cases, the ability to form sex pili and donate DNA
during conjugation results from the presence of a particular
piece of DNA called the F factor (F forfertility). The F factor
consists of about 25 genes, most required for the production
ofsex pili. The Ffactor can exist either as a plasmid or as a segment
of DNA within the bacterial chromosome.