ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: For example, in CML, assuming that mRNA levels are proportional to the number of genes in a cell, the BCRABL/ABL ratio can be represented as the ratio of a number of malignant cells to the weighted sum of normal cells (which have two copies of ABL) and malignant cells (which have one copy of ABL) [124].