During beginning fertilization of the egg the cytoplasm triggers lysosomes vesicles that release enzymes that hard the zona pellucida so that it reduces the chance of more than one sperm can penetrates the oocytes. The egg divided then undergoes meiosis ends. The nuclei of the egg and nuclei of the sperm unite the membrane falls apart and the chromosome mingles which complete fertilization. The sperm cell and egg cell each has 23 chromosomes and during fertilization it 46 somatic cell this cell is called a zygote the first cell of the future offspring.
The Zygotes undergoes mitosis 30 hours after forming, cells division occurs rapidly. The rapid cell division is called cleavage. During cleavage tiny cells move through the uterine tubes during the time of implantation cells in the interface of the blastocyst. The cell surrounding the embryo is called the placenta this organ attaches