Adaptive amplification: An inducible chromosomal instability mechanism

Adaptive mutation is an induced response to environmental stress in which m utation rates rise, producing permanent genetic changes that can adapt cell s to stress. This contrasts with neo-Darwinian views of genetic change rate s blind to environmental conditions. DNA amplification is a flexible, rever sible genomic change that has long been postulated to be adaptive. We repor t the discovery of adaptive amplification at the lac operon in Escherichia coli. Additionally, we find that adaptive amplification is separate from, a nd does not lead to, adaptive point mutation. This contradicts a prevailing alternative hypothesis whereby adaptive mutation is normal mutability in a mplified DNA. Instead, adaptive mutation and amplification are parallel rou tes of inducible genetic instability allowing rapid evolution under stress, and escape from growth inhibition.