A zygote is the initial cell formed when a sperm cell from a male fertilizes an egg cell from a female. This single cell contains genetic material from both parents, combining their DNA to create a unique organism. The zygote is the first stage of development in sexually reproducing organisms, including humans and many other animals. After fertilization, the zygote undergoes a series of divisions, known as cleavage, leading to the formation of a multicellular structure called a blastocyst. This process is crucial for the development of an embryo, which will eventually grow into a fully formed organism.