Final answer:
During the RecA-mediated postsynapsis stage, the formation of Holliday junctions occurs, enabling genetic recombination and chromosome segregation in meiosis.
Step-by-step explanation:
During the RecA-mediated postsynapsis stage in strand exchange, the formation of Holliday junctions takes place. This process involves the crossing-over or genetic recombination between nonsister chromatids of homologous chromosomes. Recombination nodules, located on the synaptonemal complex, are essential in mediating these crossover events. They direct the cleavage, modification of cut ends, and subsequent reconnection between the chromatids. As a result, chiasma formation allows homologous chromosomes to remain attached at specific points, facilitating the proper segregation of chromosomes during meiosis I.
When RecA proteins bind to single-stranded DNA, a nucleoprotein filament is formed. This filament facilitates the search and binding to homologous sequences on another DNA strand. Subsequent invasion of one DNA strand into the homologous double-stranded DNA leads to the formation of Holliday junctions, which are crucial intermediates of homologous recombination.
The final answer in 20 words: The postsynapsis stage involves formation of Holliday Junctions, essential for genetic recombination and accurate chromosome segregation in meiosis.