The Ph1 translocation leads to the fusion of two gen

The breakpoints of the Ph1 translocation are located
in the BCR gene of chromosome 22 and in
the ABL gene of chromosome 9. The translocation
leads to the fusion of these genes. The exact
locations of the breakpoints differ from patient
to patient, but in the BCR gene they are limited
to a small region of just 6 kb (thus the designation
BCR, or breakpoint cluster region). In CML,
the breakpoints lie in exons 10–12 of the BCR
gene; in acute Ph1-positive leukemias (e.g., ALL)
they lie further in the 5! direction in exon 1 or 2.
The breakpoint region in the ABL gene extends
over 180 kb between exons 1a and 1b, which are
separated by an intron.