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Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 11 - Gene Mutation, DNA Repair, and Homologous RecombinationProblem 37
Chapter 11, Problem 37

In a mouse-breeding experiment a new mutation called Dumbo is identified. A mouse with the Dumbo mutation has very large ears. It is produced by two parental mice with normal ear size. Based on this information, can you tell whether the Dumbo mutation is a regulatory mutation or a mutation of a protein-coding gene? Why or why not?

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Step 1: Begin by understanding the nature of the Dumbo mutation. The mutation results in a phenotype (large ears) that is different from the parental phenotype (normal ears). This indicates that the mutation affects gene expression or protein function.
Step 2: Consider the possibility of a regulatory mutation. Regulatory mutations typically affect the expression levels, timing, or location of a gene's activity. If the Dumbo mutation alters the expression of a gene involved in ear development, it could be a regulatory mutation.
Step 3: Consider the possibility of a mutation in a protein-coding gene. Mutations in protein-coding genes can change the structure or function of the protein itself, potentially leading to altered development or morphology, such as large ears.
Step 4: Evaluate the inheritance pattern. Since the Dumbo phenotype arises from two normal-eared parents, this suggests the mutation may be recessive. Both regulatory mutations and protein-coding mutations can exhibit recessive inheritance, so this does not conclusively distinguish between the two types.
Step 5: Conclude that based on the given information, it is not possible to definitively determine whether the Dumbo mutation is regulatory or protein-coding. Additional experiments, such as gene expression analysis or sequencing, would be required to identify the exact nature of the mutation.

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Key Concepts

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

Regulatory Mutations

Regulatory mutations occur in non-coding regions of DNA that control gene expression rather than altering the protein-coding sequence itself. These mutations can affect how much or when a gene is expressed, potentially leading to phenotypic changes without changing the protein structure. In the context of the Dumbo mutation, if the mutation affects the regulation of a gene involved in ear size, it could lead to the observed large ears.
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Protein-Coding Genes

Protein-coding genes are segments of DNA that contain the instructions for synthesizing proteins, which perform various functions in the organism. Mutations in these genes can lead to changes in the protein's structure and function, potentially resulting in observable traits. If the Dumbo mutation were a protein-coding mutation, it would imply a direct alteration in the protein responsible for ear development, rather than just a change in expression levels.
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Phenotypic Expression

Phenotypic expression refers to the observable traits or characteristics of an organism, which result from the interaction of its genotype with the environment. In this case, the large ears of the Dumbo mouse represent a phenotypic change. Understanding whether this change arises from a regulatory mutation or a protein-coding mutation is crucial for determining the underlying genetic mechanisms responsible for the trait.
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Related Practice
Textbook Question

A geneticist searching for mutations uses the restriction endonucleases SmaI and PvuII to search for mutations that eliminate restriction sites. SmaI will not cleave DNA with CpG methylation. It cleaves DNA at the restriction digestion sequence ↓ 5′−CCC GGG−3′ 3′−GGG CCC−3′ ↑ PvuII is not sensitive to CpG methylation. It cleaves DNA at the restriction sequence ↓ 5′−CAG CTG−3′ 3′−GTC GAC−5′ ↑ What common feature do SmaI and PvuII share that would be useful to a researcher searching for mutations that disrupt restriction digestion?

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Textbook Question

A geneticist searching for mutations uses the restriction endonucleases SmaI and PvuII to search for mutations that eliminate restriction sites. SmaI will not cleave DNA with CpG methylation. It cleaves DNA at the restriction digestion sequence ↓ 5′−CCC GGG−3′ 3′−GGG CCC−3′ ↑ PvuII is not sensitive to CpG methylation. It cleaves DNA at the restriction sequence ↓ 5′−CAG CTG−3′ 3′−GTC GAC−5′ ↑ What process is the researcher intending to detect with the use of these restriction enzymes?

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Textbook Question

A geneticist searching for mutations uses the restriction endonucleases SmaI and PvuII to search for mutations that eliminate restriction sites. SmaI will not cleave DNA with CpG methylation. It cleaves DNA at the restriction digestion sequence ↓ 5′−CCC GGG−3′ 3′−GGG CCC−3′ ↑ PvuII is not sensitive to CpG methylation. It cleaves DNA at the restriction sequence ↓ 5′−CAG CTG−3′ 3′−GTC GAC−5′ ↑ Explain why CpG dinucleotides are hotspots of mutation.

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Textbook Question

Considering the Dumbo mutation in Problem 37, what kinds of additional evidence would help you determine whether Dumbo is a mutation of a regulatory sequence or of a protein-coding gene?

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Textbook Question

Thinking back to the discussion of gain-of-function and loss-of-function mutations, explain why gain-of-function mutations are often dominant and why loss-of-function mutations are often recessive. Give an example of a type of gain-of-function mutation that is dominant and of a loss-of-function mutation that is recessive.

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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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