Tracking time of marker entry generates a chromosome map

In this interrupted-mating conjugation experiment, F⁻ streptomycin-resistant cells with mutations in azi, ton, lac, and gal are incubated for varying times with Hfr cells that are sensitive to streptomycin and carry wild-type alleles for these genes. (a) A plot of the frequency of donor alleles in exconjugants as a function of time after mating. (b) A schematic view of the transfer of markers (shown in different colors) with the passage of time.

[(a) Data from E. L. Wollman, F. Jacob, and W. Hayes, Cold Spring Harbor Symp. Quant. Biol. 21, 1956, 141.]