The zygote is the initial cell formed when a sperm fertilizes an egg, playing a crucial role in sexual reproduction. This single cell contains genetic material from both parents, representing the first step in the development of a new organism. As the zygote undergoes division through mitosis, it eventually forms a multicellular organism, laying the foundation for all body systems. Thus, the zygote serves as a critical link between genetic inheritance and the subsequent stages of growth and development.