- Following statements are made about double-strand break repair (DSBR)model of homologous recombination:
A. Process of DSBR recombination is triggered by introducing a double-strand break in a DNA duplex
B. In a process known as 3-end resection, the exonucleases along with a DNA helicase degrade one strand on either side of the break and generates 3′-single stranded termini
C. One strand of the donor duplex is displaced due to formation of heteroduplex DNA and generates a displacement loop (D-Loop)
D. Branch migration allows the point of crossover to move in 5′–à3′ direction of recipient strand
E. Completion of DSBR recombination may generate either crossover recombinant or non-recombinant product
Which one of the following combination of statements is correct?
(1) A, B and D (2) A, C and E
(3) A, C and D (4) A, B and EDouble-Strand Break Repair (DSBR) Model of Homologous Recombination: Key Steps and Correct Statements
The double-strand break repair (DSBR) model is a fundamental mechanism by which cells repair double-strand breaks (DSBs) in DNA through homologous recombination. This process is critical for maintaining genome stability and ensuring accurate genetic exchange during meiosis and mitosis.
Overview of the DSBR Model
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Initiation by DSB: The process starts when a double-strand break is introduced into a DNA duplex (Statement A).
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3′-End Resection: Exonucleases and helicases degrade the 5′ ends flanking the break, generating 3′ single-stranded DNA overhangs (Statement B).
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Strand Invasion and D-Loop Formation: One of the 3′ single-stranded overhangs invades a homologous DNA duplex, forming a displacement loop (D-loop) and heteroduplex DNA (Statement C).
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Branch Migration: The Holliday junction formed can migrate along the DNA, extending the region of strand exchange. This migration typically occurs in the 5′ to 3′ direction on the recipient strand (Statement D).
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Resolution: The double Holliday junctions are resolved to yield either crossover or non-crossover recombinant products (Statement E).
Evaluating the Statements
Statement Description Correctness A DSBR recombination is triggered by a double-strand break in DNA duplex Correct B 3′-end resection generates 3′ single-stranded termini Correct C Formation of heteroduplex DNA and D-loop by strand invasion Correct D Branch migration moves crossover point in 5′→3′ direction of recipient strand Correct E DSBR can generate crossover or non-crossover products Correct
Which Combination Is Correct?
All statements A, B, C, D, and E are correct based on the DSBR model. However, the options given combine subsets of these statements:
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(1) A, B, and D
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(2) A, C, and E
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(3) A, C, and D
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(4) A, B, and E
Among these, option (4) A, B, and E is the most comprehensive and correct combination because:
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A (DSB initiation) and B (3′-end resection) describe the early steps.
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E (crossover/non-crossover outcomes) describes the final resolution.
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While C and D are also correct, none of the options include all five statements.
Keywords for SEO Optimization
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Double-strand break repair (DSBR)
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Homologous recombination model
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DNA 3′-end resection
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Strand invasion and D-loop formation
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Branch migration in recombination
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Holliday junction resolution
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Crossover and non-crossover recombinants
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DNA repair mechanisms
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Genetic recombination pathways
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DNA damage response
Conclusion
The DSBR model of homologous recombination involves initiation by a double-strand break, 3′-end resection, strand invasion forming a D-loop, branch migration, and resolution into crossover or non-crossover products. Among the given options, the combination (4) A, B, and E best represents correct statements about DSBR.
Correct answer: (4) A, B, and E
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3 Comments
Neelam Sharma
November 7, 2025A, B and E
Divya rani
November 7, 2025All statements are correct.
Kajal
November 23, 2025All