A zygote is a single-celled organism that is formed when an EGG CELL and a sperm CELL fuse together. It is the first stage of development in the life cycle of a multicellular organism, and it is the result of fertilization. The EGG, which is three letters long, provides the nucleus and cytoplasm for the zygote, while the sperm, which is four letters long, provides the genetic material. The zygote then divides to form a blastocyst, which will eventually develop into an embryo.