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Ch. 15 - Gene Mutation, DNA Repair, and Transposition
All textbooksKlug 12th EditionCh. 15 - Gene Mutation, DNA Repair, and TranspositionProblem 29
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Chapter 15, Problem 29

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.
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Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr
Mutant 1: Met-Trp
Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr
Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His                                  _

Use this information to answer the following questions:

Using the genetic coding dictionary, predict the type of mutation that led to each altered protein.

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Key Concepts

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

Amino Acids and Protein Structure

Amino acids are the building blocks of proteins, and their specific sequence determines a protein's structure and function. Each amino acid is encoded by a set of three nucleotides in DNA, known as a codon. Changes in the amino acid sequence can lead to different protein properties, which is crucial for understanding mutations.
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Types of Mutations

Mutations are changes in the DNA sequence that can affect the resulting protein. Common types include point mutations (single nucleotide changes), insertions (adding nucleotides), and deletions (removing nucleotides). Each type can lead to different outcomes, such as silent mutations, missense mutations, or nonsense mutations, which can alter protein function.
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Mutations and Phenotypes

Genetic Code and Codon Usage

The genetic code is a set of rules that defines how nucleotide sequences are translated into amino acids. Each codon corresponds to a specific amino acid or a stop signal. Understanding the genetic code is essential for predicting the effects of mutations on protein sequences, as it allows for the identification of which amino acids are affected by changes in the DNA.
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Textbook Question
Imagine yourself as one of the team of geneticists who launches a study of the genetic effects of high-energy radiation on the surviving Japanese population immediately following the atom bomb attacks at Hiroshima and Nagasaki in 1945. Demonstrate your insights into both chromosomal and gene mutation by outlining a short-term and long-term study that addresses these radiation effects. Be sure to include strategies for considering the effects on both somatic and germ-line tissues.
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Textbook Question
With the knowledge that radiation causes mutations, many assume that human-made forms of radiation are the major contributors to the mutational load in humans. What evidence suggests otherwise?
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Textbook Question
Among Betazoids in the world of Star Trek®, the ability to read minds is under the control of a gene called mindreader (abbreviated mr). Most Betazoids can read minds, but rare recessive mutations in the mr gene result in two alternative phenotypes: delayed-receivers and insensitives. Delayed-receivers have some mind-reading ability but perform the task much more slowly than normal Betazoids. Insensitives cannot read minds at all. Betazoid genes do not have introns, so the gene only contains coding DNA. It is 3332 nucleotides in length, and Betazoids use a four-letter genetic code. The following table shows some data from five unrelated mr mutations. Mutation Description of Mutation Phenotype _ mr-1 Nonsense mutation in codon 829 Delayed-receiver mr-2 Missense mutation in codon 52 Delayed-receiver mr-3 Deletion of nucleotides 83–150 Delayed-receiver mr-4 Missense mutation in codon 192 Insensitive mr-5 Deletion of nucleotides 83–93 Insensitive For each mutation, provide a plausible explanation for why it gives rise to its associated phenotype and not to the other phenotype. For example, hypothesize why the mr-1 nonsense mutation in codon 829 gives rise to the milder delayed-receiver phenotype rather than the more severe insensitive phenotype. Then repeat this type of analysis for the other mutations. (More than one explanation is possible, so be creative within plausible bounds!)
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Textbook Question

Shown below are two homologous lengths of the alpha and beta chains of human hemoglobin. Consult a genetic code dictionary (Figure 13.7), and determine how many amino acid substitutions may have occurred as a result of a single nucleotide substitution. For any that cannot occur as a result of a single change, determine the minimal mutational distance.

Alpha: ala val ala his val asp asp met pro
Beta: gly leu ala his leu asp asn leu lys

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Textbook Question
It has been noted that most transposons in humans and other organisms are located in noncoding regions of the genome—regions such as introns, pseudogenes, and stretches of particular types of repetitive DNA. There are several ways to interpret this observation. Describe two possible interpretations. Which interpretation do you favor? Why?
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Textbook Question

Mutations in the IL2RG gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases in humans. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The IL2RG gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the IL2RG gene product (assume its length to be 375 amino acids).

Nonsense mutation in a coding region

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