The gametes are usually formed by the meiotic divisions. Therefore, these are haploid having half (n) the number of chromosomes. In sexual reproduction, male and female gametes fuse to form a single cell called zygote. This process is called fertilisation. The zygote formed by the fusion of two haploid gametes is thus diploid or having (2n) number of chromosomes. So, we can say that meiosis and fertilisation are the two important events in sexual reproduction that keep the number of chromosomes constant from generation to generation.