An amber mutant was grown in amber suppressor cells and plated onto normal (non-permissive) cells to score revertants (1). The analysis of the number of revertants arising from single bursts (c = 1) yielded 296 mutants in 1306864 bursts and B = 76. Thus f / c = 296 / 1306864 / 76 = 3.0 ´ 10^-6. However, T was not determined. Discarding indels, there are eight possible single mutations changing an amber stop codon to a non-stop codon. However, some might be lethal and hence not observable. For a fraction of lethal substitutions of p_L = 0.2-0.4, T = T_s = 4.8-6.4. Assuming no further selection against viable revertants and taking T_s = 5.6, m_s/n/c = 3 ´ 3.0 ´ 10^-6 / 5.6 = 1.6 ´ 10^-6. The undetermined T_s value could lead to a maximal underestimation of 5.6-fold and a maximal overestimation of 1.4-fold. Although the E(s_v) values of the reversions were unknown, this should not introduce bias here because c = 1. Data from this experiment can also be used to obtain an estimate of the mutation rate per strand copying free of selection bias using the fluctuation test null-class method.

1. Chao, L., C. U. Rang, and L. E. Wong. 2002. Distribution of spontaneous mutants and inferences about the replication mode of the RNA bacteriophage f6. J. Virol. 76:3276-3281.