Zygotes

A zygote is the single-celled organism formed at the beginning of the development of a new organism, before further cell division and differentiation. A zygote is created when a sperm cell fertilizes an egg cell. It is the first step in the development of a new individual, and is considered to be the most important phase in the development of an embryo. After its formation, the zygote divides multiple times and becomes a multicellular organism. Zygotes are essential for reproduction in both humans and other animals.