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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1:57 minutes

Problem 22b

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.

Verified step by step guidance

Understand the problem: The question asks for examples of DNA sequence changes outside exons that can lead to mutations, and how these changes affect mutant mRNA or protein. This involves understanding regulatory and structural elements of genes beyond coding regions.

Step 1: Splice site mutations - Explain that mutations in splice donor or acceptor sites (e.g., GT at the 5' end of an intron or AG at the 3' end) can disrupt splicing. This may result in intron retention, exon skipping, or the use of cryptic splice sites, leading to altered mRNA and potentially truncated or nonfunctional proteins.

Step 2: Promoter mutations - Discuss how mutations in the promoter region can affect transcription initiation. For example, a mutation in the TATA box or other regulatory elements can reduce or abolish transcription, leading to decreased or absent mRNA and protein production.

Step 3: Enhancer or silencer mutations - Highlight that mutations in enhancer or silencer regions can alter the binding of transcription factors, leading to changes in gene expression levels. This can result in overexpression, underexpression, or misexpression of the gene, affecting protein levels or function.

Step 4: Polyadenylation signal mutations - Explain that mutations in the polyadenylation signal (e.g., AAUAAA) can disrupt proper 3' end processing of mRNA. This can lead to unstable mRNA or altered protein products due to improper translation termination.

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Key Concepts

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

Introns and Exons

Introns are non-coding sequences in a gene that are transcribed into pre-mRNA but are removed during RNA splicing, while exons are the coding sequences that remain in the mature mRNA. Understanding the roles of introns and exons is crucial because mutations in introns can affect splicing, potentially leading to altered protein products even if the coding sequence remains unchanged.

Splice Site Mutations

Splice site mutations occur at the boundaries of introns and exons, affecting the recognition of these sites by the splicing machinery. Such mutations can lead to the inclusion of intronic sequences in the mRNA or the exclusion of exonic sequences, resulting in frameshift mutations or truncated proteins, which can have significant functional consequences.

Regulatory Element Mutations

Regulatory elements, such as enhancers and silencers, are DNA sequences that control the expression of genes. Mutations in these regions can alter the binding of transcription factors, leading to changes in gene expression levels. This can result in either overexpression or underexpression of the corresponding protein, potentially causing various phenotypic effects.

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Related Practice

Textbook Question

Speculate on how improved living conditions and medical care in the developed nations might affect human mutation rates, both neutral and deleterious.

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Textbook Question

The two DNA and polypeptide sequences shown are for alleles at a hypothetical locus that produce different polypeptides, both five amino acids long. In each case, the lower DNA strand is the template strand:

Based on DNA and polypeptide sequences alone, is there any way to determine which allele is dominant and which is recessive? Why or why not?

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Textbook Question

Many human genes are known to have homologs in the mouse genome. One approach to investigating human hereditary disease is to produce mutations of the mouse homologs of human genes by methods that can precisely target specific nucleotides for mutation.

Despite the homologies that exist between human and mouse genes, some attempts to study human hereditary disease processes by inducing mutations in mouse genes indicate there is little to be learned about human disease in this way. In general terms, describe how and why the study of mouse gene mutations might fail to produce useful information about human disease processes.

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Textbook Question

Numerous studies of mutations of the mouse homologs of human genes have yielded valuable information about how gene mutations influence the human disease process. In general terms, describe how and why creating mutations of the mouse homologs can give information about human hereditary disease processes.

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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

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

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?

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