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Philadelphia chromosome

(FIH-luh-DEL-fee-uh KROH-muh-some)
An abnormal version of chromosome 22 that contains a fusion of two genes, the ABL1 gene and the BCR gene. This fusion gene is made when part of the ABL1 gene on chromosome 9 breaks off and attaches to the BCR gene on chromosome 22. The protein made by the BCR::ABL1 fusion gene can cause immature white blood cells to grow uncontrollably and build up in the bone marrow and blood. The Philadelphia chromosome is found in the bone marrow cells of almost all people with chronic myelogenous leukemia and some people with acute lymphocytic leukemia or acute myelogenous leukemia.
Philadelphia chromosome; three-panel drawing shows a piece of chromosome 9 and a piece of chromosome 22 breaking off and trading places, creating a changed chromosome 22 called the Philadelphia chromosome. In the left panel, the drawing shows a normal chromosome 9 with the ABL1 gene and a normal chromosome 22 with the BCR gene. In the center panel, the drawing shows part of the ABL1 gene breaking off from chromosome 9 and a piece of chromosome 22 breaking off, below the BCR gene. In the right panel, the drawing shows chromosome 9 with the piece from chromosome 22 attached. It also shows a shortened version of chromosome 22 with the piece from chromosome 9 containing part of the ABL1 gene attached. The ABL1 gene joins to the BCR gene on chromosome 22 to form the BCR::ABL1 fusion gene. The changed chromosome 22 with the BCR::ABL1 fusion gene on it is called the Philadelphia chromosome.Enlarge this image in new window
The Philadelphia (Ph) chromosome is an abnormal chromosome that is made when pieces of chromosomes 9 and 22 break off and trade places. The ABL1 gene from chromosome 9 joins to the BCR gene on chromosome 22 to form the BCR::ABL1 fusion gene. The changed chromosome 22 with the fusion gene on it is called the Ph chromosome.
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