meiotic DNA double-strand break processing involved in reciprocal meiotic recombination

Definition

Target type: biologicalprocess

The cell cycle process in which the 5' to 3' exonucleolytic resection of the DNA at the site of the break to form a 3' single-strand DNA overhang occurs resulting in double strand break formation and repair through a double Holliday junction intermediate. [GOC:dph, GOC:tb]

Meiotic DNA double-strand break (DSB) processing is a crucial step in reciprocal meiotic recombination, a process that generates genetic diversity during sexual reproduction. This intricate pathway involves the following key steps:

1. **DSB Formation:** Specialized enzymes, including topoisomerase VI and Spo11, introduce DSBs in the DNA. These breaks are highly specific, occurring in regions called hot spots that are rich in specific DNA sequences.

2. **5' End Resection:** After DSB formation, the 5' ends of the broken DNA strands are resected by exonucleases, creating 3' single-stranded tails. These tails serve as the starting point for the homology search.

3. **Strand Invasion and D-loop Formation:** The 3' single-stranded tails, guided by the RecA homolog Rad51 and its partner Dmc1, invade the homologous chromosome. This invasion creates a displacement loop (D-loop), where the invading strand displaces one of the strands in the intact chromosome.

4. **Second End Capture:** The second broken end of the original DNA molecule is captured by the D-loop structure, facilitated by the same homologous recombination machinery. This capture event leads to the formation of a double Holliday junction (HJ), a key intermediate in recombination.

5. **Holliday Junction Resolution:** The HJ structure is resolved by enzymes such as resolvases or the structure-specific endonuclease, resulting in the exchange of genetic material between the two homologous chromosomes.

6. **Crossover Formation:** During HJ resolution, the crossover (CO) outcome, characterized by a physical exchange of DNA segments between chromosomes, can occur with a certain probability. COs contribute significantly to genetic diversity.

7. **Non-crossover Formation:** Alternatively, HJ resolution can also lead to a non-crossover (NCO) outcome, where no physical exchange of DNA segments occurs. NCOs contribute to the maintenance of genetic linkage between genes on the same chromosome.

The precise mechanism of meiotic DSB processing is tightly regulated and involves the coordinated action of numerous proteins. This intricate process ensures the accurate and efficient exchange of genetic information during meiosis, contributing to the generation of novel genetic combinations in offspring and driving the evolutionary process.'
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