Sexual reproduction occurs through the stages of meiosis. Meiosis itself has two different rounds.
In the first round, the cell grows, copies its chromosomes, and readies itself for division (Interphase). Then, the chromosomes themselves condense and match up perfectly with a partner (specifically called a homologue partner) in Prophase I. These partners trade parts in what is called crossing over. This increases genetic diversity because it creates new combinations of chromosomes with unique alleles. After Prophase I, the chromosomes prepare for splitting (Metaphase I), and the homologues are then separated and moved to different sides of the cell (Anaphase I). Lastly, the chromosomes successfully arrive at the opposite ends, forming two daughter cells (Telophase I and Cytokinesis). This ends the first round of meiosis.
In the second round, the cell skips Interphase, but goes through the rest of the phases, resulting in 4 cells.
