Conjugal transfer can also be used for genetic mapping. By using many different hfr strains, each with the F factor integrated at a different part of the E. colichromosome, the positions of many genes were mapped. These studies showed that the genetic map of the E. coli chromosome is circular.
During conjugal transfer, genes closer to the site of F integration are transferred first. By disrupting the mating at different times, one can determine which genes are closer to the integration site. Thus on the E. coli chromosome, genes are mapped in terms of minutes (i.e., the time it takes to transfer to recipient).
For example, for an hfr strain with the F factor integrated at 0 min on the E. colimap, conjugal transfer to a female recipient would transfer
leuACBD at 1.7 min
pyrH at 4.6 min
proAB at 5.9 min
bioABFCD at 17.5 min.
Use of hfr strains with different sites of integration (initiation of transfer) allows the entire circular genome to be mapped (Fig. 1.11). 0/100 is thrABC.
Figure 1.11.Circular genetic map of E. coli.