The biological process that leads to the formation of gametes is called meiosis. Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four distinct haploid cells from an original diploid cell. It occurs in two main stages: meiosis I and meiosis II. This process is crucial for sexual reproduction, as it produces egg and sperm cells necessary for fertilization and genetic diversity. Additionally, meiosis introduces genetic variation through mechanisms such as crossing over and independent assortment of chromosomes.