Fertilization is the biological process involving the union of two specialized haploid cells, generally referred to as gametes, resulting in the formation of a diploid zygote. This process requires the fusion of the outer membranes of the contributing cells, allowing the genetic material from both sources to combine into a single nucleus. Following successful fusion, the zygote immediately begins rapid mitotic division, initiating the formation of an embryonic structure. The immediate biological events following initial fusion are characterized by the establishment of a new, unified genome and the commencement of cell division to create the necessary cellular organization for subsequent development.