Accelerated degradation study: control genes: BCR-ABL/control gene ratios. The average BCR-ABL/ABL ratios per fixed volume of cDNA for each of the 4 reference materials are shown after storage at the designated temperatures for 10 months. The data for BCR-ABL/BCR and BCR-ABL/GUSB were very similar, as were the data at 6 months' storage.