Meiosis is a crucial part of sexual reproduction because it reduces the chromosome number for gametes. During meiosis, a single diploid cell undergoes two rounds of division to produce four haploid cells. This reduction in chromosome number is essential because it ensures that when two gametes (sperm and egg) fuse during fertilization, the resulting zygote will have the correct number of chromosomes, which is characteristic of the species.
If meiosis did not occur, the chromosome number would double with each generation, leading to an unsustainable and potentially harmful increase in genetic material. By halving the chromosome number, meiosis maintains genetic stability and allows for genetic diversity through the process of recombination, where homologous chromosomes exchange genetic material. This diversity is vital for the adaptation and evolution of species.