Chronic myeloid leukemia (CML) originates from a hematopoietic stem cell affected by a reciprocal translocation between chromosomes 9 and 22, which results in the formation of the BCR-ABL1 fusion gene in the short derivative of chromosome 22 (Ph chromosome)1. The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.