→ All the events of sexual reproduction that take place before the fusion of gametes are included in pre-fertilisation category. It includes gametogenesis and gamete transfer. At the time of gamete formation, meiocytes undergo meiotic division. As a result of meiotic division, the number of chromosomes in the daughter cells (i.e., in the gametes) reduce to half and thus from the diploid meiocytes thus, haploid gametes are formed. → Post-fertilisation events refer to all the events of sexual reproduction taking place after fertilisation, that is, after the formation of zygote. After fertilisation, cleavage occurs.