Reciprocal translocation in the Philadelphia Chromosome
Standard Chromosomes 9 &
22 are shown at left: they are subject to breakage at
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. [Reciprocal shortening of
Chromosome 9 was not as obvious in early studies].
Juxtaposition of the abl and bcr loci
interferes with cancer suppressor genes, 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 ©2014 by Steven M. Carr