Final answer:
During Prophase I of meiosis, the nuclear envelope breaks down, chromosomes condense, spindle formation begins, homologous chromosomes pair, and crossing over occurs, leading to increased genetic diversity.
Step-by-step explanation:
During Prophase I of meiosis, several key events occur in preparation for cellular division. The nuclear envelope begins to break down, allowing the chromosomes to condense and become more visible. As this happens, the centrioles start migrating to opposite poles of the cell, and the formation of the mitotic spindle is initiated.
A distinguishing feature of this phase is the pairing of homologous chromosomes, which is a critical process unique to meiosis and does not occur during mitosis or meiosis II. Additionally, an important genetic mechanism called crossing over takes place, where homologous chromosomes exchange genetic material, increasing genetic diversity. As Prophase I progresses, the nucleolus vanishes, signaling further preparation for the division processes to follow.