FIG. 1.

Adaptive point mutation and adaptive gene amplification are separate outcomes that arise with different kinetics. Point mutants have compensatory frameshift reversions in the lac gene (19, 61) and also carry high frequencies of other mutations genome wide (24, 57, 70). lac-amplified clones carry 20 to 50 tandem repeats of 7- to 40-kb DNA segments spanning the leaky lac frameshift allele, which allow growth on lactose medium without a compensatory frameshift mutation (30). lac-amplified clones do not carry high levels of extra mutations genome wide (30). Shown is a cumulative plot. The lac-amplified clones comprise typically ≥40% of new colonies from day 8 onward (30). Data are from reference 30.