Hfr cell

Hfr Cell

An Hfr cell (High frequency of recombination) is a bacterium with a conjugative plasmid integrated into its chromosomal DNA. This integration allows the bacterium to transfer part of its chromosomal DNA to a recipient cell during bacterial conjugation. The process of Hfr formation and the subsequent genetic exchange play a crucial role in bacterial genetics and the study of gene mapping.

Diagram illustrating the process of Hfr recombination.

Formation of Hfr Cells

Hfr cells are formed when an F plasmid (fertility plasmid) integrates into the bacterial chromosome through a process called homologous recombination. This integration occurs at specific sites on the chromosome, known as insertion sequences, which are homologous to sequences on the F plasmid. Once integrated, the F plasmid is referred to as an episome.

Mechanism of Gene Transfer

During bacterial conjugation, an Hfr cell can transfer part of its chromosomal DNA to a recipient F- cell. The transfer begins at the origin of transfer (oriT) on the integrated F plasmid and proceeds in a linear fashion. However, because the entire chromosome is rarely transferred, the recipient cell usually remains F- but acquires new genetic material from the donor.

Significance in Genetic Mapping

Hfr cells are instrumental in genetic mapping of bacterial chromosomes. By analyzing the sequence and timing of gene transfer during conjugation, researchers can determine the relative positions of genes on the chromosome. This technique, known as interrupted mating, has been used extensively in Escherichia coli to map its genetic material.

Differences from F+ Cells

While both Hfr and F+ cells contain the F plasmid, the key difference lies in the integration of the plasmid into the chromosome in Hfr cells. F+ cells have the F plasmid as an independent, circular DNA molecule, whereas in Hfr cells, the plasmid is integrated into the host's chromosomal DNA.

Related Pages

• Bacterial conjugation
• F plasmid
• Gene mapping
• Escherichia coli