CML is a myeloproliferative disorder characterized by a cytogenic abnormality involving the fusion of the breakpoint cluster region (BCR) gene on long arm of chromosome 9 and ABL proto-oncogene-1 (ABL1) on long arm of chromosome 22, resulting in the characteristic t(9;22) (q34;q11) translocation called the Philadelphia chromosome (Ph). The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.