What cell forms after a sperm cell fuses with an egg cell during fertilization?

During fertilization, when a sperm cell successfully fuses with an egg cell, the resulting cell is known as a zygote. The zygote is the first stage of development in a new organism and contains a complete set of chromosomes—half contributed by the sperm and half by the egg. This single-cell structure is crucial as it initiates the developmental process that will eventually lead to the formation of an embryo.

The zygote undergoes numerous cell divisions, known as cleavage, leading to the development of multicellular forms. While the embryo arises later as the zygote develops and differentiates, the term "embryo" refers to subsequent stages of development, not the initial cell formed at fertilization. Similarly, gametes refer to the reproductive cells (sperm and egg), and a blastocyst is a later structure formed a few days post-fertilization that is involved in implantation into the uterine wall. Therefore, the formation of a zygote is a foundational and essential step following the fusion of the sperm and egg, marking the beginning of a new organism's life cycle.