Strictly speaking, making an exact copy of a bacterial population is impossible. Stored samples are frozen with glycerol as a cryoprotectant (which E. coli cells can metabolize), and are revived in DM1000. Thus, a frozen population that is being revived is exposed to a resource environment that contains both glycerol and a far higher glucose concentration than is found in DM25. As these conditions are very different than those the population experienced during the LTEE prior to archiving, outgrowth during revival is an unavoidable perturbation. However, this procedure has been designed to ameliorate and reduce the effects of this perturbation so as to maintain the representative genetic diversity within the population sample, minimize changes in the frequencies of different genotypes, and avoid further evolution caused by new mutations.