What is the initial cell formed after fertilization?

The initial cell formed after fertilization is known as the zygote. This refers to the single cell that results when a sperm cell successfully fertilizes an egg cell. The zygote consists of genetic material from both the mother and father, combining to create a new organism's unique genetic identity.

Following fertilization, the zygote undergoes a series of cell divisions and developments. Within a few days, it develops into a blastocyst, which is essential for implantation in the uterine wall, but at the point of fertilization, it is still classified as a zygote. After the blastocyst stages, the cells will further differentiate and develop into an embryo, which represents the early stages of development leading up to the fetal stage. The term "fetus" refers to a later stage of development when the major structures and organ systems of the body have formed. Thus, the zygote is the very first step in this entire developmental process.