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

17. Mutation, Repair, and Recombination

Induced Mutations

Genetics

17. Mutation, Repair, and Recombination

Induced Mutations

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2:28 minutes

Problem 22a

Textbook Question

Xeroderma pigmentosum (XP) is an autosomal recessive condition characterized by moderate to severe sensitivity to ultraviolet (UV) light. Patients develop multiple skin lesions on UV-exposed skin, and skin cancers often develop as a result. XP is caused by deficient repair of DNA damage from UV exposure. Many genes are known to be involved in repair of UV-induced DNA damage, and several of these genes are implicated in XP. What genetic phenomenon is illustrated by XP?

Verified step by step guidance

Understand the genetic basis of Xeroderma pigmentosum (XP): XP is an autosomal recessive condition caused by mutations in genes responsible for repairing UV-induced DNA damage.

Recognize that multiple genes are involved in the repair of UV-induced DNA damage. These genes encode proteins that function in nucleotide excision repair (NER), a pathway critical for correcting UV-induced DNA lesions.

Identify the genetic phenomenon illustrated by XP: Since mutations in any one of several genes can lead to the same condition (XP), this is an example of genetic heterogeneity. Genetic heterogeneity occurs when mutations in different genes produce the same phenotype.

Consider the implications of genetic heterogeneity: In XP, different patients may have mutations in different genes, but all exhibit the same clinical symptoms due to the shared disruption of the DNA repair pathway.

Conclude that understanding genetic heterogeneity is important for diagnosing and treating XP, as different mutations may require different therapeutic approaches or genetic counseling strategies.

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Key Concepts

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

Autosomal Recessive Inheritance

Autosomal recessive inheritance is a pattern of genetic transmission where two copies of a mutated gene, one inherited from each parent, are necessary for an individual to express a trait or disorder. In the case of Xeroderma pigmentosum (XP), individuals must inherit two defective copies of the genes responsible for DNA repair to exhibit symptoms, highlighting the importance of both alleles in the manifestation of the condition.

DNA Repair Mechanisms

DNA repair mechanisms are cellular processes that identify and correct damage to the DNA molecules that encode an organism's genome. In XP, the deficiency in these repair pathways, particularly those that fix UV-induced damage, leads to an accumulation of mutations, resulting in skin lesions and increased cancer risk. Understanding these mechanisms is crucial for grasping how XP develops.

Genetic Phenotype

A genetic phenotype refers to the observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences. In XP, the phenotype is characterized by extreme sensitivity to UV light and the development of skin lesions and cancers, illustrating how specific genetic mutations can lead to distinct clinical manifestations.

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Related Practice

Textbook Question

Using your knowledge of DNA repair pathways, choose the pathway that would be used to repair the following types of DNA damage. Explain your reasoning.

A thymine dimer induced as a result of UV exposure

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Textbook Question

Common baker's yeast (Saccharomyces cerevisiae) is normally grown at 37°C, but it will grow actively at temperatures down to approximately 25°C. A haploid culture of wild-type yeast is mutagenized with EMS. Cells from the mutagenized culture are spread on a complete-medium plate and grown at 25°C. Six colonies (1 to 6) are selected from the original complete-medium plate and transferred to two fresh complete-medium plates. The new complete plates (shown) are grown at 25°C and 37°C. Four replica plates are made onto minimal medium or minimal plus adenine from the 25°C complete-medium plate. The new plates are grown at either 25°C or 37°C and the growth results are shown.

Classify the nature of the mutations in colonies 1, 2, and 5.

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Textbook Question

Common baker's yeast (Saccharomyces cerevisiae) is normally grown at 37°C, but it will grow actively at temperatures down to approximately 25°C. A haploid culture of wild-type yeast is mutagenized with EMS. Cells from the mutagenized culture are spread on a complete-medium plate and grown at 25°C. Six colonies (1 to 6) are selected from the original complete-medium plate and transferred to two fresh complete-medium plates. The new complete plates (shown) are grown at 25°C and 37°C. Four replica plates are made onto minimal medium or minimal plus adenine from the 25°C complete-medium plate. The new plates are grown at either 25°C or 37°C and the growth results are shown.

Which colonies are prototrophic and which are auxotrophic? What growth information is used to make these determinations?

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Textbook Question

What can you say about colony 4?

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Multiple Choice

Which of the following is an example of an induced mutation?

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Multiple Choice

Which of the following mutagens wedges between DNA bases to disrupt the helix structure?