Final answer:
Recipient cells typically remain F minus after mixing with Hfr cells because the full F plasmid is often not transferred due to the transient nature of bacterial conjugation, which typically allows only part of the chromosome, not the entire F plasmid, to transfer.
Step-by-step explanation:
When Hfr cells are mixed with F minus cells, the recipient cells can acquire traits from the Hfr strain, but they usually remain F minus. This is because the conjugation process, which involves the transfer of genetic material, often does not include the complete transfer of the F plasmid. The Hfr cells have the F plasmid integrated into their chromosome, which allows them to transfer chromosomal genes to the F minus cell. However, because bacterial conjugation is usually a brief event and the bacterial chromosome is large, only a portion of the chromosome, including genes close to the integration site of the F plasmid, is typically transferred before the mating bridge breaks.
This means that although the F minus cell receives new genetic information, it often does not receive the entire F plasmid required to become F plus. The result is that, while the recipient cell may exhibit some characteristics of the donor Hfr strain due to the acquired genes, it does not become an Hfr cell capable of initiating further conjugation events with other F minus cells.