The difference between Hfr and F+ strains is
Hfr cells can become F+, but F+ cells cannot become Hfr.
The fertility plasmid is integrated into the host cell chromosomal DNA in Hfr cells while the fertility plasmid is independent in F+ cells.
Hfr cells are able to convert F- recipient cells to F+, but F+ cells are not able to convert F- recipient cells to F+.
Hfr are able to conjugate with only other Hfr cells, and F+ cells are able to conjugate only with other F+ cells.
The correct answer and explanation is :
The correct answer is:
The fertility plasmid is integrated into the host cell chromosomal DNA in Hfr cells, while the fertility plasmid is independent in F+ cells.
Explanation:
In bacterial genetics, the F factor (fertility factor) is a plasmid that determines the ability of a bacterium to transfer genetic material during conjugation. There are two primary types of bacterial cells based on the presence and state of the F factor: Hfr cells and F+ cells.
- F+ Cells:
- In F+ cells, the F factor exists as an independent plasmid in the cytoplasm of the bacterial cell. This plasmid carries the genes necessary for the formation of a sex pilus, a structure that allows for the transfer of genetic material during conjugation. F+ cells can transfer the F factor to F- cells (recipient cells) through conjugation, converting them into F+ cells.
- F+ cells are not able to transfer chromosomal DNA to another cell during conjugation. Their role is limited to transferring the fertility plasmid itself.
- Hfr Cells:
- In Hfr cells (high-frequency recombination cells), the F factor is integrated into the chromosomal DNA of the bacterium. This integration enables the Hfr cell to initiate conjugation and transfer not only the F factor but also chromosomal DNA. The transfer of chromosomal DNA can lead to genetic recombination in the recipient cell.
- Because the F factor is integrated into the chromosome, the transfer is initiated from a specific site on the bacterial chromosome. When an Hfr cell conjugates with an F- cell (a recipient cell lacking the F factor), a portion of the chromosome (including part of the F factor) is transferred to the F- cell. This can sometimes result in partial genetic transformation, but the F- cell is typically not converted into an F+ cell, since the full F factor is usually not transferred.
- Key Differences:
- F+ cells can only transfer the F plasmid itself to an F- cell, while Hfr cells can transfer large portions of the bacterial chromosome along with the F factor to an F- cell.
- F+ cells remain F+ after conjugation, whereas Hfr cells have the potential to cause recombination in recipient cells and may remain Hfr after conjugation, depending on the transfer process.
- Hfr cells are not restricted to conjugating with only other Hfr cells, but they do typically form conjugation bridges with F- cells to transfer their chromosomal material.
Thus, the key distinction lies in the integration of the F factor into the chromosome in Hfr cells, while in F+ cells, the F factor remains a separate plasmid.