561 17.5 Cancer: the genetics of aberrant cell number regulation With modern techniques for pedigree analysis, familial tendencies toward certain kinds of cancer can be matched with molecular markers such as microsatellites; in several cases, this process has led to the successful identiFcation of a mutated gene. Alternatively, many types of tumors have characteristic chromosomal translocations or deletions of particular chromosomal re-gions. In some cases, these chromosomal rearrangements are so reliably a part of a particular cancer that they can be used for diagnosis. ±or example, 95 percent of pa-tients with chronic myelogenous leukemia (CML) have a characteristic translocation between chromosomes 9 and 22. This translocation, called the Philadelphia chro-mosome after the city where the translocation was Frst described, is a critical part of the CML diagnosis. How-ever, not all tumor-promoting mutations are speciFc to a given type of cancer. Rather, the same mutations seem to
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