Shortened chromosome 22 (22q-) resulting from reciprocal translocation t(9;22)(q34;q211); occurs in 90%Ð95% of cases of chronic myelogenous leukemia, 20% of cases of adult acute lymphocytic leukemia, and 5% of cases of pediatric acute lymphocytic leukemia. Change causes fusion of BCR gene on chromosome 22 to ABL gene on chromosome 9, disrupting proto-oncogene c-abl on chromosome, which encodes for tyrosine kinase ABL (part of ras signaling pathway).