Translocation t(9;22)(q34;q11) and fusion products. The Ph is a shortened chromosome 22 that results from the transposition of 3′-ABL segments on chromosome 9 to 5′-BCR segments on chromosome 22. Whereas breakpoint locations on chromosome 9 appear rather constant 5′ of ABL exon a2, several breakpoint cluster regions have been identified along the BCR gene on chromosome 22. Depending on which breakpoints are involved on chromosome 22, differently sized segments from the BCR gene are joined together with the 3′-sequences of the ABL gene. The translocation thus results in fusion mRNA molecules of different length (e1a2, b2a2, b3a2, e19a2) and, subsequently, chimeric protein products with variable molecular weights and presumably function (p190, p210, p230) (see text for details).