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

Types of Mutations

Genetics

17. Mutation, Repair, and Recombination

Types of Mutations

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1:24 minutes

Problem 23a

Textbook Question

Mutations in the CFTR gene result in cystic fibrosis in humans, a condition in which abnormal secretions are present in the lungs, pancreas, and sweat glands. The gene was mapped to a 500-kb region on chromosome 7 containing three candidate genes.
Using your knowledge of the disease symptoms, how would you distinguish between the candidate genes to decide which is most likely to encode the CFTR gene?

Verified step by step guidance

Step 1: Understand the disease symptoms associated with cystic fibrosis, such as abnormal secretions in the lungs, pancreas, and sweat glands. These symptoms suggest that the CFTR gene is involved in processes related to ion transport and fluid balance.

Step 2: Analyze the functions of the three candidate genes within the 500-kb region on chromosome 7. Look for evidence that one of the genes is involved in ion transport, particularly chloride ion transport, as this is a hallmark of CFTR gene function.

Step 3: Examine the expression patterns of the candidate genes. The CFTR gene is expected to be expressed in tissues affected by cystic fibrosis, such as the lungs, pancreas, and sweat glands. Identify which gene has expression patterns matching these tissues.

Step 4: Investigate whether mutations in any of the candidate genes have been previously linked to cystic fibrosis symptoms. This can be done by reviewing genetic studies or databases that associate specific mutations with the disease.

Step 5: Perform functional studies, such as gene knockout or overexpression experiments, to determine which candidate gene's disruption leads to phenotypes resembling cystic fibrosis. This will help confirm the identity of the CFTR gene.

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Key Concepts

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

Gene Function and Protein Encoding

Genes encode proteins that perform specific functions in the body. Understanding the role of the CFTR gene is crucial, as it encodes a protein that regulates chloride and bicarbonate ions across epithelial cell membranes. Mutations in this gene disrupt normal ion transport, leading to the symptoms of cystic fibrosis, such as thick mucus production and respiratory issues.

Mutation Types and Their Effects

Mutations can be classified into several types, including missense, nonsense, and frameshift mutations, each affecting protein function differently. Identifying the type of mutation in the candidate genes can help determine which gene is most likely responsible for cystic fibrosis. For instance, a nonsense mutation may lead to a nonfunctional protein, while a missense mutation might alter the protein's function.

Phenotypic Correlation

Phenotypic correlation involves linking genetic variations to observable traits or symptoms. In the context of cystic fibrosis, analyzing the symptoms and their severity can help identify which candidate gene is most likely the CFTR gene. By comparing the expression patterns and functional outcomes of the candidate genes with the known symptoms of cystic fibrosis, one can make an informed decision about the most likely gene involved.

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Textbook Question

The human β-globin wild-type allele and a certain mutant allele are identical in sequence except for a single base-pair substitution that changes one nucleotide at the end of intron 2. The wild-type and mutant sequences of the affected portion of pre-mRNA are

This is one example of how DNA sequence change occurring somewhere other than in an exon can produce mutation. List other kinds of DNA sequence changes occurring outside exons that can produce mutation. In each case, characterize the kind of change you would expect to see in mutant mRNA or mutant protein.

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Textbook Question

Speculate about the way in which this base substitution causes mutation of β-globin protein.

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Textbook Question

The fluctuation test performed by Luria and Delbrück is consistent with the random mutation hypothesis. Briefly describe their experiment and identify how the results match the prediction of the random mutation hypothesis. What would have to be different about the experimental results for them to agree with the prediction of the adaptive mutation hypothesis?

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Textbook Question

Mutations in the CFTR gene result in cystic fibrosis in humans, a condition in which abnormal secretions are present in the lungs, pancreas, and sweat glands. The gene was mapped to a 500-kb region on chromosome 7 containing three candidate genes.

How would you prove that your chosen candidate is the CFTR gene?

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Textbook Question

In a bacterial culture in which all cells are unable to synthesize leucine (leu⁻), a potent mutagen is added, and the cells are allowed to undergo one round of replication. At that point, samples are taken, a series of dilutions are made, and the cells are plated on either minimal medium or minimal medium containing leucine. The first culture condition (minimal medium) allows the growth of only leu⁺ cells, while the second culture condition (minimal medium with leucine added) allows growth of all cells. The results of the experiment are as follows:

What is the rate of mutation at the locus associated with leucine biosynthesis?

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Textbook Question

In this chapter, three features of genes or of DNA sequence that contribute to the occurrence of mutational hotspots were described. Identify those three features and briefly describe why they are associated with mutational hotspots.

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Textbook Question

Briefly compare the production of DNA double-strand breaks in bacteria versus the double-strand breaks that precede homologous recombination.

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Textbook Question