Which of the following statements is NOT TRUE regarding an Hfr X F bacterial cross? A The recipient usually remains F B. Large segments of the donor Hfr chromosome can be transferred into the F- cell: C. The F chromosome can undergo recombination with piece of the donor chromosome D. The donor cell becomes P E. Hfr X F crosses can be used t0 order bacterial genes on a linear map:
The Correct Answer and Explanation is:
The statement that is NOT TRUE regarding an Hfr X F bacterial cross is:
D. The donor cell becomes F.
Explanation:
In an Hfr (High frequency of recombination) X F (Fertility factor) bacterial cross, the key steps involve the transfer of genetic material from an Hfr cell to an F- (recipient) cell. Here’s why each statement is true or false:
A. The recipient usually remains F.
- True. The F- cell, which initially lacks the F plasmid, typically remains F- after the cross. The transferred genetic material does not usually include the entire F plasmid, so the recipient cell does not become F+.
B. Large segments of the donor Hfr chromosome can be transferred into the F- cell.
- True. In an Hfr X F cross, the F plasmid is integrated into the bacterial chromosome of the donor Hfr cell. During conjugation, large segments of the donor’s chromosome (which includes the F plasmid) can be transferred to the recipient F- cell. The process starts from the origin of the F plasmid and can extend to distant parts of the donor chromosome.
C. The F chromosome can undergo recombination with a piece of the donor chromosome.
- True. The transferred DNA can undergo recombination with the recipient’s chromosome. This is an essential aspect of the Hfr X F cross because it allows the mapping of bacterial genes based on how frequently they recombine with the recipient chromosome.
D. The donor cell becomes F.
- False. In an Hfr X F cross, the donor cell does not become F+. The donor (Hfr) retains its integrated F plasmid in the chromosome. The F plasmid is not usually transferred in its entirety, so the donor remains Hfr, not F+.
E. Hfr X F crosses can be used to order bacterial genes on a linear map.
- True. Hfr X F crosses are crucial for creating genetic maps. By measuring the time at which different genes are transferred to the recipient cell, researchers can create a linear map of bacterial genes.
In summary, the donor does not become F in an Hfr X F cross. Therefore, D is the incorrect statement.
