Fertilization:
Fertilization is the process by which a sperm cell fuses with an egg cell, resulting in the formation of a zygote. It is a crucial step in sexual reproduction that leads to the development of a new individual.

Events following fertilization:
After fertilization, a series of events occur that are essential for the development of the embryo. These events can be categorized into three stages: cleavage, implantation, and embryogenesis.

Cleavage:
Cleavage is the rapid division of the zygote into multiple cells. It involves a series of mitotic divisions without any significant growth. The zygote undergoes cleavage to form a solid ball of cells called a morula. The morula further divides and forms a hollow ball of cells called a blastula.

Implantation:
Implantation is the process by which the blastula attaches and embeds itself into the wall of the uterus. It occurs around 6-7 days after fertilization. The blastula undergoes changes and forms a structure known as the blastocyst. The blastocyst consists of an inner cell mass and an outer layer of cells called the trophoblast. The trophoblast helps in the attachment of the blastocyst to the uterine wall. Once attached, the trophoblast cells invade the uterine lining and form finger-like projections called villi. These villi are responsible for the exchange of nutrients and waste between the mother and the developing embryo.

Embryogenesis:
Embryogenesis is the process of development of the embryo from the blastocyst. It involves the differentiation and specialization of cells into various tissues and organs. The inner cell mass of the blastocyst undergoes gastrulation, where it forms three germ layers: ectoderm, mesoderm, and endoderm. These germ layers give rise to different tissues and organs of the body.

During embryogenesis, important structures such as the notochord, neural tube, and somites are formed. The notochord serves as the axial support for the developing embryo and gives rise to the backbone. The neural tube develops into the brain and spinal cord, while the somites give rise to the muscles and skeletal system.

Further development of the embryo involves organogenesis, where organs and systems such as the cardiovascular, respiratory, digestive, and nervous systems develop. This process is highly complex and requires precise coordination of various cellular and molecular events.

In conclusion, fertilization is the fusion of sperm and egg cells, leading to the formation of a zygote. The events following fertilization include cleavage, implantation, and embryogenesis. Cleavage involves rapid cell division, while implantation involves the attachment of the blastocyst to the uterine wall. Embryogenesis is the process of differentiation and specialization of cells, leading to the formation of various tissues and organs of the developing embryo.