Chromosome 9 is made up of about 141 million DNA building blocks (base pairs) and represents approximately 4.5 percent of the total DNA in cells. Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 9 likely contains 800 to 900 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body. Changes in the structure of chromosome 9 have been found in many types of cancer. These changes, which occur only in cancer cells, usually involve a loss of part of the chromosome or a rearrangement of chromosomal material. For example, a loss of part of the long (q) arm of chromosome 9 has been identified in some types of brain tumor. It is unclear how these chromosomal changes are related to the development and growth of cancers. A rearrangement (translocation) of genetic material between chromosomes 9 and 22 is associated with several types of blood cancer known as leukemias. This chromosomal abnormality, which is commonly called the Philadelphia chromosome, is found only in cancer cells. It fuses part of a specific gene from chromosome 22 (the BCR gene) with part of another gene from chromosome 9 (the ABL1 gene). The protein produced from these fused genes signals tumor cells to continue dividing abnormally and prevents them from adequately repairing DNA damage. The Philadelphia chromosome has been identified in most cases of a slowly progressing form of blood cancer called chronic myeloid leukemia (CML). It also has been found in some cases of more rapidly progressing blood cancers known as acute leukemias. The presence of the Philadelphia chromosome can help predict how a cancer will progress and provides a target for molecular therapies.
https://seer.cancer.gov/seertools/hemelymph/51f6cf56e3e27c3994bd530c/
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