F-Plasmids and Sexduction

Just as F-plasmids can be integrated into the chromosome, so they can also be occasionally excised from the Hfr-chromosome to produce a free plasmid. Sometimes, the excision does not occur in a precise manner by exact reversal of the integration. Instead, some portion of the chromosomal DNA bordering the integrated F-DNA is included in the excised F-plasmid. Such aberrant F-plasmids containing a fragment of the chromosome are designated as F’-plasmids. 

Different Hfr-strains in which F-plasmid has been integrated at different sites of chromosome may give rise to different F’-plasmids each having a different chromosomal fragment attached to it. The F’-plasmids can be transferred to F– cells by the usual conjugation process. Thereby, the recipients not only acquire the F-plasmid DNA, but also the chromosomal fragment carried by the F’-plasmid. This process of chromosomal gene transfer via F’-plasmids from a donor to a recipient is known as sexduction or F-duction. The recipient cell becomes partial diploid (or merodiploid) for the genes carried by the chromosomal fragment attached to the F-plasmid.