File:Hfr Recombination.png

English: 1. The insertion sequences (yellow) on both the F factor plasmid and the chromosome have similar sequences, allowing the F factor to insert itself into the genome of the cell. This is called homologous recombination and creates an Hfr (high frequency of recombination) cell.

2. The Hfr cell forms a pilus and attaches to a recipient F- cell. 3. A nick in one strand of the Hfr cell’s chromosome is created. 4. DNA begins to be transferred from the Hfr cell to the recipient cell while the second strand of its chromosome is being replicated. 5. The pilus detaches from the recipient cell and retracts. The Hfr cell ideally wants to transfer its entire genome to the recipient cell. However, due to its large size and inability to keep in contact with the recipient cell, it is not able to do so. 6. a. The F- cell remains F- because the entire F factor sequence was not received. Since no homologous recombination occurred, the DNA that was transferred is degraded by enzymes.

b. In very rare cases, the F factor will be completely transferred and the F- cell will become an Hfr cell.