The generation of various recombinants by crossing over in different regions
Figure 5-17: The diagram shows how genes can be mapped by recombination in E. coli. In exconjugants, selection is made for merozygotes bearing the leu+ marker, which is donated late. The early markers (arg+ and met+) may or may not be inserted, depending on the site where recombination between the Hfr fragment and the F− chromosome takes place. The frequencies of events diagrammed in parts a and b are used to obtain the relative sizes of the leu- arg and argmet regions. Note that, in each case, only the DNA inserted into the F− chromosome survives; the other fragment is lost.
ANIMATED ART: Bacterial conjugation and mapping by recombination
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