Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination

Problem 38

Chapter 11, Problem 38

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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Analyze the location of the Dumbo mutation within the genome. If the mutation is found in a non-coding region, such as a promoter, enhancer, or other regulatory sequence, it suggests a regulatory mutation. If the mutation is located within a protein-coding region, it may affect the structure or function of the protein.

Examine the expression levels of the gene associated with the Dumbo mutation. If the mutation affects a regulatory sequence, you might observe changes in the timing, location, or overall levels of gene expression. Use techniques like quantitative PCR or RNA sequencing to measure gene expression.

Investigate the protein product of the gene. If the mutation is in a protein-coding region, it could lead to changes in the amino acid sequence, potentially altering the protein's structure or function. Perform protein analysis using methods like Western blotting or mass spectrometry to detect these changes.

Perform functional assays to test the impact of the mutation. For example, if the mutation is suspected to be in a regulatory sequence, you could use reporter gene assays to measure the activity of the regulatory element. If the mutation is in a protein-coding region, test the activity or stability of the protein in vitro or in vivo.

Use genetic complementation or rescue experiments. Introduce a wild-type copy of the gene or regulatory sequence into the organism with the Dumbo mutation. If the phenotype is rescued, this provides evidence for the role of the mutated region in causing the observed effects.

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Key Concepts

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

Regulatory Sequences

Regulatory sequences are regions of DNA that control the expression of genes. They can include promoters, enhancers, and silencers, which interact with transcription factors to increase or decrease gene expression. Understanding whether the Dumbo mutation affects these sequences can help determine if it alters gene regulation rather than the protein product itself.

Protein-Coding Genes

Protein-coding genes are segments of DNA that contain the instructions for synthesizing proteins. Mutations in these genes can lead to changes in the amino acid sequence of the resulting protein, potentially affecting its function. Identifying whether the Dumbo mutation occurs within a protein-coding region is crucial for understanding its impact on phenotype.

Functional Evidence

Functional evidence refers to experimental data that demonstrate the effects of a mutation on gene expression or protein function. This can include assays like reporter gene studies, RNA sequencing, or protein assays. Gathering such evidence can clarify whether the Dumbo mutation influences regulatory mechanisms or directly alters protein coding.

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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 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

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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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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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.

Classify the nature of the mutations in colonies 1, 2, and 5.

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