What is the initial cell called that results from the fertilization of an egg by a sperm?

The initial cell that results from the fertilization of an egg by a sperm is known as a zygote. This single-cell entity forms immediately after the male sperm successfully penetrates the female ovum, leading to the fusion of their genetic material.

The zygote subsequently undergoes a series of mitotic divisions, known as cleavage, as it begins its development into a multi-cellular organism. During this process, it eventually transforms into a blastocyst, which marks a later stage in development when the embryo is ready to implant into the uterine wall. Before reaching the zygote stage, the sperm and egg are referred to as gametes; however, they are not classified as a single entity until fertilization occurs. The term embryo refers to the developing organism after it has progressed beyond the zygote and is often used after implantation occurs.

Therefore, the correct identification of the initial fertilized cell as a zygote is essential in understanding the early stages of human development.