Why do most cancers require the mutation of multiple genes?

Sanders 3rd Edition
Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics
Problem B.8Do you think it is important that participation in community-based genetic screening be entirely voluntary? Why or why not?
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Key Concepts
Informed Consent
Ethical Principles in Genetics
Community-Based Genetic Screening
Based on what you read in this chapter, Can a tumor arise from a single mutated cell? Are all the cells in a tumor identical?
Describe how CRISPR–Cas has been modified to create a genome-editing tool.
The inheritance of certain mutations of BRCA1 can make it much more likely that a woman will develop breast or ovarian cancer in her lifetime. Can you say with certainty that a woman inheriting a mutation of BRCA1 will definitely develop breast or ovarian cancer in her lifetime? Why or why not?
The inheritance of certain mutations of BRCA1 can make it much more likely that a woman will develop breast or ovarian cancer in her lifetime. In addition to inheriting a BRCA1 mutation, what else must happen for a woman to develop breast or ovarian cancer?
Discuss the advantages (and possible disadvantages) of the different approaches to reverse genetics.