The Philadelphia Chromosome and the (t9;22) translocation. What we refer to as the "Philadelphia" Chromosome is actually the little bit of junk that's left of the 22nd chromosome after the translocation. The novel BCR-ABL gene product causes the runaway proliferation of the cell carrying the mutation. The BCR-ABL gene can be detected in the circulating WBCs of people carrying this translocation. Roll the cursor over the image to see the translocation.