XYLT2 and chronic myelogenous leukemia, BCR-ABL1 positive: Since non-transgenic mice of the three relevant SOS genotypes (WT, SOS1-KO, and SOS2-KO) tested at different ages always showed a similar percentage distribution in all these blood cell populations (Figure 3D), our data clearly indicate that the functional contribution of SOS1 (but not SOS2) is critically required for the development of CML in p210BCR/ABL transgenic mice.