Final answer:
An Hfr cell is responsible for initiating chromosome transfer from one E. coli to another during the process of bacterial conjugation, which allows for high frequency of recombination and gene mapping.
Step-by-step explanation:
An Hfr cell can initiate chromosome transfer from one E. coli to another. This process occurs when the F plasmid, which can form a part of the E. coli's chromosome, begins the transfer to an F- (recipient) cell. As part of this complex process, a conjugation tube is formed between the Hfr cell and the F- cell, and a single strand of the Hfr cell's chromosomal DNA is transferred. This transfer can include not only the F plasmid DNA but also additional chromosomal genes located near the F plasmid integration site. However, due to the transient nature of cell contact during conjugation, it's unlikely that the entire chromosome will be transferred, with genes closest to the integration site being transferred first.
The formation of Hfr cells is a key event in bacterial conjugation because it allows for the high frequency of recombination and the potential for gene mapping in E. coli, providing a deeper understanding of bacterial genetics before the era of genome sequencing.