What significant event occurs in prophase 1 of meiosis?

In prophase 1 of meiosis, a crucial event is the pairing of homologous chromosomes, a process known as synapsis. During this phase, each chromosome aligns with its homologous partner, allowing for the formation of tetrads, which consist of four chromatids. This close association is essential for the subsequent genetic recombination or crossing over, which takes place in late prophase 1. The homologous chromosomes exchange genetic material at points called chiasmata, leading to increased genetic diversity in the resulting gametes.

This synapsis is particularly significant because it ensures that when meiosis continues through the subsequent phases, the segregation of chromosomes is accurate, ultimately leading to the formation of haploid cells. Thus, this event is foundational for maintaining genetic variability in sexually reproducing organisms.

In contrast, while the disappearance of the nuclear envelope and the migration of centrioles to opposite poles occur during prophase, these events are not the defining characteristics of prophase 1. The separation of chromatids into individual chromosomes happens in anaphase, not in prophase.