Hfr strains that differ in integrated F factor orientation and site of integration are used to construct consolidated bacterial chromosome maps. The data below show the order of gene transfer for five strains.

Hfr Strain       Order of Gene Transfer (First → Last)
Hfr A                oriT–thr–leu–azi–ton–pro–lac–ade
Hfr B                oriT–mtl–xyl–mal–str–his
Hfr C                oriT–ile–met–thi–thr–leu–azi–ton
Hfr D                oriT–his–trp–gal–ade–lac–pro–ton
Hfr E                oriT–thi–met–ile–mtl–xyl–mal–str

Draw a consolidated map of the bacterial chromosome. (Hint: Begin by placing the insertion site for Hfr A at the 2 o'clock position and arranging the genes thr–leu–azi- . . . in clockwise order.)

Key Concepts

Hfr Strains

Hfr (high frequency of recombination) strains are bacterial strains that have the F factor integrated into their chromosome. This integration allows them to transfer chromosomal genes to a recipient bacterium during conjugation. The orientation and site of integration of the F factor can affect the order in which genes are transferred, making Hfr strains valuable for mapping bacterial chromosomes.

Gene Transfer Order

The order of gene transfer in Hfr strains is determined by the sequence in which genes are located on the bacterial chromosome relative to the origin of transfer (oriT). During conjugation, genes closest to oriT are transferred first, followed by those further away. Analyzing the transfer order from different Hfr strains allows researchers to deduce the relative positions of genes on the chromosome.

Consolidated Chromosome Maps

Consolidated chromosome maps are graphical representations that depict the relative positions of genes on a bacterial chromosome based on data from multiple Hfr strains. By comparing the gene transfer orders from different strains, researchers can create a comprehensive map that illustrates the arrangement of genes, aiding in the understanding of bacterial genetics and gene function.