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| Modern Genetic Analysis Chapter 9. The Genetics of Bacteria and Phages Bacterial Conjugation Figure 9-7. Interrupted-mating conjugation experiments with E. coli. F cells that are strr are crossed with Hfr cells that are strs. The F cells have a number of mutations (indicated by the genetic markers azi, ton, lac, and gal) that prevent then from carrying out specific metabolic steps. However, the Hfr cells are capable of carrying out all these steps. At different times after the cells have been mixed, samples are withdrawn, disrupted in a blender to break conjugation between cells, and plated on media containing streptomycin. The antibiotic kills the Hfr cells but allows the F cells to grow and to be tested for their ability to carry out the four metabolic steps. (a) A plot of the frequency of recombinants for each metabolic marker as a function of time after mating. Transfer of the donor allele for each metabolic step depends on how long conjugation is allowed to continue. (b) A schematic view of the transfer of markers over time. (Part a modified from E. L. Wollman, F. Jacob, and W. Hayes, Cold Spring Harbor Symposia on Quantitative Biology 21, 1956, 141.)

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