GENES THAT AFFECT CANCER
It is important to distinguish two general types of genes that affect cancer. Some genes affect the susceptibility to develop cancer. Increased susceptibility to cancer may be inherited (see later discussion) just like any other genetic defect. In addition, there are two classes of genes directly involved in producing cancers as the result of somatic mutations. These are the oncogenes and the tumor-suppressor genes or anti-oncogenes.
A major difference between oncogenes and anti-oncogenes depends on the fact that animals are diploid and possess two copies of each gene. Oncogenes are cancer-causing genes, and mutant oncogenes promote the development of cancer cells. Mutations in oncogenes are dominant, and so a single oncogenic mutation in just one of a pair of genes is sufficient to give an effect. The second, wild-type copy of the gene cannot make up for the defect.
In contrast, tumor suppressor genes have a negative effect on cancer development. As their name suggests, they normally suppress division of cancer cells. To allow cancers to grow, both copies of a tumor suppressor gene must be inactivated by mutation. A defective mutation in just one copy of a tumor suppressor gene has no effect; that is, these are recessive mutations.
Because cancers are due to mutations, the techniques used in genomic analysis are widely used in analyzing cancers at the genetic level. These include the use of DNA sequencing, PCR and microarrays, and have already been described, DNA Synthesis, and Genomics.
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