Prophase I is the first stage of meiosis, a type of cell division that reduces the chromosome number by half. During this phase, the chromosomes condense and become visible under a microscope. Each chromosome pairs with its homologous partner, forming structures called tetrads. This pairing is crucial for genetic recombination. In addition to pairing, crossing over occurs during prophase I, where segments of DNA are exchanged between homologous chromosomes. This process increases genetic diversity in the resulting gametes. Prophase I is a complex and essential step in the formation of sperm and egg cells in organisms.