Answer :
To understand the question about Hfr and F+ strains, let's first define these terms:
F+ Strain: In bacteria, particularly E. coli, an F+ strain refers to a bacterial cell that contains a plasmid known as the 'F factor' or 'fertility factor'. This plasmid allows the bacterial cell to produce a sex pilus, which can connect to other bacterial cells to transfer genetic material. The key characteristic of an F+ strain is that the F factor is present as a separate plasmid and not integrated into the bacterial chromosome.
Hfr Strain: Hfr stands for 'high frequency of recombination'. This occurs when the F factor is integrated into the bacterial chromosome itself. This integration allows for more efficient and frequent recombination of genetic material during conjugation with F- strains (bacteria without the F factor).
Now, let's evaluate the statements to identify which one is incorrect:
F+ strain has F factor integrated in the bacterial genome.
- This is incorrect. An F+ strain contains the F factor as a separate plasmid, not integrated into the genome.
Hfr strain has F factor integrated in the bacterial genome.
- This is correct. In an Hfr strain, the F factor is integrated into the bacterial chromosome.
F+ strain has low recombination frequency.
- This is correct. Because the F factor is not integrated into the chromosome in F+ strains, the recombination frequency is typically lower compared to Hfr strains.
Hfr strain does not convert an F- strain to an F+ strain.
- This is correct. During mating with an F- strain, an Hfr strain can transfer chromosomal genes, but it typically does not transfer the entire F factor, so the recipient remains F- after the partial transfer.
The statement that does not correctly describe these strains is:
1. F+ strain has F factor integrated in the bacterial genome.
