E1. If the physiological adaptation theory had been correct, mutations should have occurred after the cells were plated on the media containing T1 bacteriophages. Since the same numbers of bacteria were streaked on each plate, we would have expected to see roughly the same number of resistant colonies on all of the plates. The number of resistant colonies would not have depended on the timing of the mutation. In contrast, what was actually observed was quite different. If a random mutation occurred early in the growth of a bacterial population (within a single tube), there were a large number of T1-resistant colonies on the plate. Whereas, if a random mutation occurred late, or not at all, there were few or no colonies on the plate. E2. When cells from a master plate were replica plated onto two plates containing selective media with the T1 phage, T1-resistant colonies were observed at the same locations on both plates. These results indicate that the mutations occurred randomly while on the master plate (in the absence of T1) rather than occurring as a result of exposure to T1. In other words, mutations are random events, and selective conditions may promote the survival of mutant
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