Shortly after the zygote is formed, it begins the processes of duplication and division, each resulting new cell has the same number of chromosomes as was contained in the zygote. A fertilized egg is called a zygote until it divides into 16 cells, forming a ball-shaped structure called a morula. The events during the zygote stage involves integration of both parents' DNA into the cell nucleus and the beginning of rapid cell division, or cleavage.