Hfr strain bacterial has F factor integrated into its genome when these bacteria undergo conjugation and the copy F factor is transferred to the recipient bacterium (F- strain).
Luca Cavalli-Sforza first described the Hfr strain.
During mating, the Hfr bacterium attempts to transfer all of its DNA to the F bacterium.
However, because mating bridges are structurally fragile, gene transfer is often incomplete.
Therefore, the recipient bacterium may receive only part of the bacterial genome of the donor Hfr bacterium and, rarely, the entire genome.
Conjugation process:
The Hfr strain can transfer several host genes to the recipient.
Sexual pili contact the recipient's F cells and attract them.
The donor chromosome is transmitted as ss-DNA from the transmission initiation site.
The gene closest to the origin is transmitted first.
The integrated plasmid segments are at the beginning and end of the transferred DNA.
To transfer the entire plasmid, the entire bacterial gene must first be transferred, but the donor and recipient cells are separated before the genome and plasmid are completely transferred.
Normally, only part of the F plasmid, called the starting segment, is transferred with the adjacent chromosomal gene.
The transferred DNA will be double-stranded.
Donor DNA is integrated into recipient cell DNA by homologous recombination.
The recipient currently has the transferred gene but remains F while the donor cell remains HFr.
Recipient cells do not become F + donor cells because only part of the F plasmid is transferred, but donor cells remain as Hfr strains.
