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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 16
Chapter 11, Problem 16

A strain of E. coli is identified as having a null mutation of the RecA gene. What biological property do you expect to be absent in the mutant strain? What is the molecular basis for the missing property?

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Understand the role of the RecA gene: The RecA protein is essential for homologous recombination and DNA repair in E. coli. It facilitates the exchange of genetic material between homologous DNA sequences and is involved in the SOS response to DNA damage.
Identify the biological property affected: A null mutation in the RecA gene means the RecA protein is non-functional or absent. This would result in the inability of the mutant strain to perform homologous recombination and repair DNA damage effectively.
Explain the molecular basis: RecA binds to single-stranded DNA (ssDNA) and forms a nucleoprotein filament. This filament searches for homologous sequences in double-stranded DNA (dsDNA) and facilitates strand exchange, a critical step in DNA repair and recombination. Without RecA, this process cannot occur.
Discuss the consequences of the mutation: The mutant strain would be highly sensitive to DNA-damaging agents (e.g., UV radiation or chemical mutagens) because it cannot repair DNA damage efficiently. Additionally, the SOS response, which is triggered by extensive DNA damage, would be impaired as RecA is required to activate the LexA repressor cleavage.
Summarize the missing property: The absence of RecA results in the loss of homologous recombination and an impaired ability to repair DNA damage, leading to genomic instability and increased sensitivity to environmental stressors.

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Key Concepts

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

RecA Protein Function

RecA is a crucial protein in bacteria that facilitates homologous recombination and DNA repair. It plays a key role in the SOS response, allowing cells to repair damaged DNA and maintain genomic integrity. A null mutation in the RecA gene results in the absence of this protein, impairing the cell's ability to effectively respond to DNA damage.
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Homologous Recombination

Homologous recombination is a process by which genetic material is exchanged between similar or identical DNA molecules. This mechanism is essential for repairing double-strand breaks in DNA and for genetic diversity during meiosis. In the absence of RecA, the mutant E. coli strain would be unable to perform homologous recombination, leading to increased susceptibility to DNA damage.
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SOS Response

The SOS response is a global response to DNA damage in bacteria, activating a set of genes involved in DNA repair and mutagenesis. RecA protein is central to this response, as it helps to initiate the repair processes. Without RecA, the mutant strain would lack the ability to mount an effective SOS response, resulting in an inability to repair DNA damage and increased cell death.
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Related Practice
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 protein that is shorter than the wild-type protein but does not have any amino acid changes in the portion produced.

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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 null mutation that does not produce any functional protein product.

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Textbook Question

A 1-mL sample of the bacterium E. coli is exposed to ultraviolet light. The sample is used to inoculate a 500-mL flask of complete medium that allows growth of all bacterial cells. The 500-mL culture is grown on the benchtop, and two equal-sized samples are removed and plated on identical complete-medium growth plates. Plate 1 is immediately wrapped in a dark cloth, but plate 2 is not covered. Both plates are left at room temperature for 36 hours and then examined. Plate 2 is seen to contain many more growing colonies than plate 1.

Thinking about DNA repair processes, how do you explain this observation?

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Textbook Question

Describe the difference between DNA transposons and retrotransposons.

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Textbook Question

How are flanking direct repeat sequences created by transposition?

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Textbook Question

Using the adenine–thymine base pair in this DNA sequence

...GCTC...

...CGAG...

Give the sequence after a transition mutation.

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