Total cholesterol in blood is reported as the number of milligrams (mg) of cholesterol per 100 milliliters (mL) of blood. The normal range is 180–220 mg/100 mL. A gene mutation altering the function of cell-surface cholesterol receptors restricts the ability of cells to collect cholesterol from blood and draw it into cells. This defect results in elevated blood cholesterol levels. Individuals who are heterozygous for a mutant allele and a wild-type allele have levels of 300–600 mg/100 mL, and those who are homozygous for the mutation have levels of 800–1000 mg/100 mL. Identify the genetic term that best describes the inheritance of this form of elevated cholesterol level, and justify your choice.
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
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
17. Mutation, Repair, and Recombination
Types of Mutations
Problem 14c
Textbook Question
Several types of mutation are identified and described in the chapter. These include (1) promoter mutation, (2) splice site mutation, (3) missense mutation, (4) frameshift mutation, and 5) nonsense mutation. Match the following mutation descriptions with the type(s) of mutations listed above. More than one mutation type might match a description.
A mutation that produces a mutant protein that differs from the wild-type protein at one amino acid position.

1
Understand the problem: The question asks us to identify the type of mutation that results in a mutant protein differing from the wild-type protein at one amino acid position. This means we need to focus on mutations that alter the amino acid sequence of the protein.
Review the mutation types: Recall the definitions of the mutation types provided: (1) Promoter mutation affects gene expression but does not directly alter the protein sequence. (2) Splice site mutation can lead to improper mRNA splicing, potentially altering the protein sequence. (3) Missense mutation changes one codon, leading to a single amino acid substitution. (4) Frameshift mutation alters the reading frame, potentially changing many amino acids. (5) Nonsense mutation introduces a premature stop codon, truncating the protein.
Focus on the description: The mutation described in the problem results in a single amino acid change. This aligns most closely with a missense mutation, as it specifically causes a single codon change leading to one amino acid substitution.
Eliminate unrelated mutation types: Promoter mutations do not affect the protein sequence. Frameshift mutations and nonsense mutations typically cause more extensive changes than a single amino acid substitution. Splice site mutations could potentially cause a single amino acid change, but they are less specific to this description compared to missense mutations.
Conclude the matching: The mutation described in the problem is best matched with a missense mutation, as it directly causes a single amino acid substitution in the protein sequence.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Missense Mutation
A missense mutation is a type of point mutation where a single nucleotide change results in the substitution of one amino acid for another in the protein sequence. This alteration can affect the protein's function, depending on the role of the specific amino acid in the protein's structure and activity. For example, if the substituted amino acid is critical for the protein's active site, the mutation may lead to a loss of function.
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Wild-Type Protein
The wild-type protein refers to the normal, non-mutated version of a protein that is typically produced by a gene. It serves as the standard against which mutant proteins are compared. Understanding the wild-type protein's structure and function is essential for assessing the impact of mutations, such as missense mutations, on protein activity and overall cellular function.
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Protein Structure and Function
The structure of a protein is intricately linked to its function, as the specific arrangement of amino acids determines how the protein folds and interacts with other molecules. Changes in the amino acid sequence, such as those caused by missense mutations, can lead to alterations in the protein's three-dimensional shape, potentially disrupting its biological activity. This relationship is crucial for understanding the consequences of genetic mutations on health and disease.
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