What is the primary event in Metaphase I of meiosis?

During Metaphase I of meiosis, the primary event involves the alignment of pairs of homologous chromosomes along the metaphase plate at the cell's equatorial plane. This is a critical step, as it ensures that the homologous chromosomes are correctly positioned to be separated later in the process of meiosis. The homologous chromosomes are held together by the synaptonemal complex, which facilitates their alignment prior to separation.

This alignment is crucial for genetic diversity, as it allows for independent assortment of the chromosomes, leading to a mix of maternal and paternal chromosomes in the resulting gametes. This random distribution is a key feature of meiosis, contributing to genetic variation in sexually reproducing organisms.

Understanding this process is essential for grasping how meiosis contributes to the generation of genetic diversity and the overall function of sexual reproduction. The other options refer to events that occur at different stages of meiosis, such as the condensation of chromosomes, separation of sister chromatids, or reformation of the nuclear membrane, which do not specifically occur during Metaphase I.