Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

19. Cancer Genetics

Cancer Mutations

Genetics

19. Cancer Genetics

Cancer Mutations

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1:17 minutes

Problem 9

Textbook Question

Define tumor-suppressor genes. Why is a mutated single copy of a tumor-suppressor gene expected to behave as a recessive gene?

Verified step by step guidance

Understand the definition of tumor-suppressor genes: Tumor-suppressor genes are genes that encode proteins responsible for regulating cell growth and division, repairing DNA damage, and ensuring proper cell cycle checkpoints. Their primary role is to prevent uncontrolled cell proliferation, which can lead to cancer.

Recognize the normal function of tumor-suppressor genes: These genes typically act as 'brakes' in the cell cycle, ensuring that cells do not divide uncontrollably. Examples include genes like TP53, RB1, and BRCA1.

Explain the concept of recessive behavior in mutations: For a tumor-suppressor gene to lose its function completely, both copies (alleles) of the gene must be mutated. This is because the presence of one functional copy can still produce enough protein to maintain normal cellular function. This is why a single mutated copy behaves as recessive.

Discuss the 'two-hit hypothesis': This hypothesis, proposed by Alfred Knudson, explains that both alleles of a tumor-suppressor gene must be inactivated (mutated) for cancer to develop. The first mutation may be inherited or occur sporadically, while the second mutation typically occurs later in life.

Summarize why a single mutated copy is insufficient to cause cancer: A single functional copy of the tumor-suppressor gene can still perform its role in regulating cell growth and preventing tumor formation. Therefore, the mutation behaves recessively, as the loss of function only occurs when both copies are mutated.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Tumor-Suppressor Genes

Tumor-suppressor genes are segments of DNA that encode proteins responsible for regulating cell growth and division. They act as a safeguard against uncontrolled cell proliferation, helping to prevent the formation of tumors. When functioning properly, these genes can repair DNA damage or initiate apoptosis, the process of programmed cell death, thereby maintaining cellular integrity.

Recessive Alleles

A recessive allele is a variant of a gene that does not manifest its trait in the presence of a dominant allele. In the context of tumor-suppressor genes, if one copy of the gene is mutated, the normal copy can often compensate for the loss of function. Therefore, the effects of the mutation are only observed when both copies of the gene are mutated, which is why they are considered to behave recessively.

Two-Hit Hypothesis

The two-hit hypothesis, proposed by Alfred Knudson, explains how tumor-suppressor genes contribute to cancer development. It posits that both alleles of a tumor-suppressor gene must be inactivated for a tumor to develop. This means that an individual with one normal and one mutated allele will not exhibit tumor formation until the second allele is also mutated, reinforcing the recessive nature of these genes in cancer biology.

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Related Practice

Textbook Question

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?

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Textbook Question

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?

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Textbook Question

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?

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Textbook Question

Go to the website http://www.cancer.gov and select 'Cancer Types' on the top menu bar. Scroll down to 'Breast Cancer' and click. Select 'Cases & Prevention' from the options. Click 'More information' and select 'BRCA Mutations: Cancer Risk and Genetic Testing'. Use the information on this page to answer the following questions. Are there measures a woman with a positive result can take to lessen her chances of developing cancer or to catch a cancer early in its development?

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Textbook Question

Go to the website http://www.cancer.gov and select 'Cancer Types' on the top menu bar. Scroll down to 'Breast Cancer' and click. Select 'Cases & Prevention' from the options. Click 'More information' and select 'BRCA Mutations: Cancer Risk and Genetic Testing'. Use the information on this page to answer the following questions. With regard to the results of genetic testing for BRCA1 and BRCA2 mutations, what is meant by a 'positive result'?

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Textbook Question

Go to the website http://www.cancer.gov and select 'Cancer Types' on the top menu bar. Scroll down to 'Breast Cancer' and click. Select 'Cases & Prevention' from the options. Click 'More information' and select 'BRCA Mutations: Cancer Risk and Genetic Testing'. Use the information on this page to answer the following questions. What are the approximate percentage increases in risk of having breast cancer and of having ovarian cancer for women inheriting harmful mutations of BRCA1 and BRCA2 compared with the risks in the general population?

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Textbook Question

Go to the website http://www.cancer.gov and select 'Cancer Types' on the top menu bar. Scroll down to 'Breast Cancer' and click. Select 'Cases & Prevention' from the options. Click 'More information' and select 'BRCA Mutations: Cancer Risk and Genetic Testing'. Use the information on this page to answer the following questions. What features of family history increase the likelihood that a woman will have a harmful mutation of BRCA1 or BRCA2?

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Textbook Question

Describe the steps by which the TP53 gene responds to DNA damage and/or cellular stress to promote cell-cycle arrest and apoptosis. Given that TP53 is a recessive gene and is not located on the X chromosome, why would people who inherit just one mutant copy of a recessive tumor-suppressor gene be at higher risk of developing cancer than those without the recessive gene?

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