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Cancer and Genome Evolution 19.3 & 19.5 Lesson 4.7 Genes Associated with Cancer • Oncogenes – cancer-causing genes in certain retroviruses – Mutated versions of proto-oncogenes – genes that code for proteins that stimulate normal cell growth and division – Caused by the following • Movement of DNA within the genome • Amplification of a proto-oncogene • Point mutations Genes Associated with Cancer • Tumor-Suppressor Genes – genes whose normal product INHIBITS cell division – Proteins produced help prevent uncontrolled cell growth Cell Signal Interference • Ras gene – codes for the Ras protein, which relays a signal from a growth factor receptor on a plasma membrane to protein kinases – At the end of this cycle is a protein that stimulates the cell cycle • P53 gene – “guardian angel of the genome” – codes for DNA repair enzymes, and enzymes to stop the cell cycle if there is damage • P. 372 Cancer Development Process 1. Normal epithelial cells lose the tumorsuppressing gene (small, benign growth) 2. Activation of ras oncogene (larger, benign growth) 3. Loss of p53 gene and additional mutations (malignant tumor) Inherited Predisposition to Cancer • Someone inheriting an oncogene or mutant allele of a tumor-suppressing gene is one step closer to accumulating the necessary mutations of cancer to develop • 15% of colorectal cancers are inherited • 5-10% of breast cancer is inherited How the Genome Evolves • Evolutionarily, genome would have started with minimum genes only necessary for survival and reproduction • What happened to cause the diverse genome we have today? – Duplication (polyploidy – extra sets of chromosomes) – Errors in meiosis (crossover between chromatids that switch genes) – Exon duplication and shuffling (possible change in reading frame)