Figure 2.—

Distribution of fitness effects caused by single-nucleotide substitutions in bacteriophage f1. The frequency histogram of the 100 mutations is shown. Note that the fitness effect of lethal mutations is s = −1. The effect of each individual mutation is provided in Table S1. Shown superimposed is the best-fitting probability density function for viable, nonbeneficial mutations (a log-normal distribution with the parameter values shown in Table 3).