During which stage of prophase I does the synaptonemal complex begin to form?

The synaptonemal complex begins to form during the zygotene stage of prophase I in meiosis. This complex is crucial because it facilitates the pairing of homologous chromosomes, a process known as synapsis. As the homologous chromosomes come together, the synaptonemal complex acts as a protein structure that stabilizes and aligns them closely, allowing for proper genetic exchange and recombination in subsequent stages.

The formation of the synaptonemal complex is essential for homologous recombination, where segments of DNA are exchanged between the paired chromosomes, leading to genetic diversity in the resulting gametes. This stage follows the leptotene phase, where chromosomes begin to condense and become visible but have not yet paired. After the zygotene phase comes pachytene, where significant genetic recombination occurs, followed by the diplotene stage, where the synaptonemal complex begins to disassemble as the chromosomes start to separate.