HFGRII immediately acquires drug resistance during long-term halofuginone selection. HFGRII was drug phenotyped at 27, 34, 41, and 50 generations along the selection. The black arrows identify when the corresponding halofuginone drug concentration was increased to 7, 21, 42, and 140 nM. Resistance is quantified as the fold-increase in EC50 of the total population over the EC50 of the Dd2 parental line. EC50s were determined by a tritiated hypoxanthine incorporation dose-response assay. Error bars denote standard deviation.