Chapter 14, Problem 13P

This problem concerns Fig. 14.14, which illustrates the experiment performed by Lederberg and Tatum that first indicated the existence of bacterial conjugation.

a.

Strain A had mutations in two genes, while strain B had three mutations. The reason is that Lederberg and Tatum wanted to ensure that the phenomenon they were examining did not involve reversion of mutations. Explain the logic behind this aspect of their experimental design, assuming that the rate of reversion of a single gene is one in 10 million (1 in 10 ) cells. How did these investigators know that the cells they found after mixing the two cultures were indeed not due to reversion?

b.

The experiment shown in Fig. 14.14 did not inform the investigators which strain was the donor and which was the recipient. Describe a way in which they could modify this experiment to answer this question