Final answer:
An Hfr cell is formed when the F plasmid integrates into the bacterial chromosome. This can result in the transfer of chromosomal DNA through conjugation. The F' plasmid formed from the integrated F plasmid can also be transferred to recipient F cells.
Step-by-step explanation:
An Hfr cell is formed when the F plasmid integrates into the bacterial chromosome through recombination, resulting in a high frequency of recombination when genetic information is transferred to recipient F cells through conjugation. On conjugation, the integrated F plasmid may be imprecisely excised from the chromosome, producing an F' plasmid that carries some chromosomal DNA. This F' plasmid can be transferred to an F cell by conjugation, introducing the DNA to the recipient cell's bacterial chromosome.