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 18

Chapter 11, Problem 18

How are flanking direct repeat sequences created by transposition?

Verified step by step guidance

Understand the concept of transposition: Transposition is the movement of transposable elements (TEs) within the genome. These elements can insert themselves into new locations, often creating structural changes in the DNA sequence.

Learn about flanking direct repeats: Flanking direct repeats are short, identical sequences found on both sides of a transposable element after it inserts into the genome. These repeats are not part of the transposable element itself but are created during the insertion process.

Examine the mechanism of insertion: When a transposable element inserts into a target site, the target DNA is cleaved asymmetrically, creating single-stranded overhangs. These overhangs are complementary and will later be filled in during DNA repair.

Understand the role of DNA polymerase: After the transposable element is inserted, DNA polymerase fills in the single-stranded gaps created by the asymmetric cleavage. This process duplicates the sequence at the target site, resulting in the flanking direct repeats.

Recognize the significance of flanking direct repeats: These repeats are a hallmark of transposition and can be used to identify the presence and activity of transposable elements in the genome. They also provide insight into the molecular mechanisms of transposition.

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Key Concepts

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

Transposition

Transposition is the process by which a segment of DNA, known as a transposon or 'jumping gene', moves from one location in the genome to another. This movement can occur through a 'cut and paste' mechanism or a 'copy and paste' mechanism, leading to the insertion of the transposon at a new site. Understanding transposition is crucial for grasping how flanking direct repeat sequences are formed.

Flanking Direct Repeat Sequences

Flanking direct repeat sequences are short, identical sequences of DNA that are found on either side of a transposon after it has inserted into a new location. These repeats are created during the transposition process when the transposon integrates into the target DNA, causing the host DNA to be cut and then repaired, resulting in the duplication of the adjacent sequences. This phenomenon is a hallmark of transposable elements.

DNA Repair Mechanisms

DNA repair mechanisms are cellular processes that correct damage to the DNA structure. When a transposon inserts itself into a new location, the host cell's repair machinery is activated to fix the breaks in the DNA. This repair often results in the duplication of the sequences adjacent to the insertion site, leading to the formation of flanking direct repeat sequences, which are essential for understanding the impact of transposition on genomic architecture.

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Repair Pathways

Related Practice

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?

Textbook Question

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?

Textbook Question

Describe the difference between DNA transposons and retrotransposons.

Textbook Question

Using the adenine–thymine base pair in this DNA sequence

...GCTC...

...CGAG...

Give the sequence after a transition mutation.

Textbook Question

Using the adenine–thymine base pair in this DNA sequence

...GCTC...

...CGAG...

Give the sequence after a transversion mutation.