iGen3 16-12

Reciprocal translocation in the Philadelphia Chromosome

    Standard Chromosomes 9 & 22 are shown at left: they are subject to breakage at the abi 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. [The reciprocal lengthening of the long arm of Chromosome 9 was not obvious in early studies].

    Juxtaposition of the abl and bcr loci interferes with oncogenes (cancer suppressor genes) in the same region, which results in a specific form of cancer, Chronic Myologenous Leukemia (CML). The Philadelphia Chromosome was one of the first genetic conditions shown to be directly associated with cancer.

Figure ©2010 PJ Russell, iGenetics 3rd ed.; all text material ©2016 by Steven M. Carr