Repair of Double-Strand Breaks During Meiosis in Saccharomyces cerevisiae: Homologous Chromosome as Template

Meiotic recombination is a vital process in sexually reproducing organisms, ensuring genetic diversity and proper chromosome segregation. In the yeast Saccharomyces cerevisiae, programmed double-strand breaks (DSBs) initiate meiotic recombination, which is repaired through highly regulated mechanisms.

How Are Meiotic DSBs Repaired in S. cerevisiae?

• DSB Formation:
  Meiotic DSBs are introduced by the Spo11 protein complex at specific hotspots on chromosomes.

• Template for Repair:
  Unlike mitotic cells that often use sister chromatids for repair, meiotic DSBs in S. cerevisiae are predominantly repaired using the homologous chromosome (homologue) as the template rather than the sister chromatid.

• Purpose of Using Homologous Chromosome:
  This interhomolog repair promotes genetic recombination (crossing over), which increases genetic diversity and ensures proper segregation of homologous chromosomes during meiosis I.

• Molecular Evidence:
  Studies mapping DSB sites and recombination events (e.g., chromosome III) confirm that repair occurs via interaction with the homologue, not the sister chromatid.

Why Not Non-Homologous End Joining or Sister Chromatid?

• Non-Homologous End Joining (NHEJ):

  • NHEJ is generally suppressed during meiosis to favor homologous recombination, which is more precise and essential for crossover formation.

• Sister Chromatid as Template:

  • Although sister chromatids are identical and available post-replication, meiotic cells preferentially use the homologue to promote genetic diversity.

Is Meiotic DSB Repair Associated with High Mutation Frequency?

• Meiotic recombination is a high-fidelity process, tightly regulated to minimize mutations.

• While gene conversion and crossover events alter genetic combinations, they do not generally increase mutation rates.

• Thus, meiotic DSB repair is not typically associated with a high frequency of mutations.

Summary of Options

Correct Answer

(3) occurs mostly using the homologous chromosome as a template

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• DNA repair during meiosis

• Interhomolog recombination

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Conclusion

In the yeast Saccharomyces cerevisiae, repair of meiotic double-strand breaks occurs mostly via homologous recombination using the homologous chromosome as the template. This mechanism is essential for generating genetic diversity and ensuring accurate chromosome segregation during meiosis. Non-homologous end joining and sister chromatid-based repair are not the primary pathways during meiosis, and the process is not associated with a high mutation frequency.

Correct answer: (3) occurs mostly using the homologous chromosome as a template