Reciprocal translocation in CML (Chronic Myologenous Lukemia):
the Philadelphia Chromosome

    Standard Chromosomes 9 & 22 are shown at left: they are subject to breakage at the abl and bcr loci, respectively. The so-called Philadelphia Chromosome is detectable cytologically as an extra G-group chromosome due to the apparent shortening of the F-group Chromosome 22 by a reciprocal exchange with Chromosome 9. Juxtaposition of the abl and bcr loci interferes with cancer suppressor genes (oncogenes), and results in a Chronic Myologenous Leukemia.

    Philadelphia Chromosome
was one of the first genetic conditions shown to be associated with cancer.

Figure 2012 TA Brown, Introduction to Genetics (1st ed.); additional text 2013 by Steven M. Carr