Figure 1.

The generation of mosaic and homogenous mutant plaques. In the first example (Upper), a lesion created within the cell line forms a mutation in the bacterium during phage replication. A lesion fixed into a mutation during the first round of phage replication produces a mosaic plaque containing a 1:1 ratio of mutant to wild-type phage, as indicated after replating the plaque. In the second example (Lower), a mutation sustained within the cell line leads to the formation of a homogenous mutant plaque, which is also made evident on replating.