Final answer:
An egg and sperm are haploid cells that fuse through the process of fertilization, creating a zygote with a complete set of chromosomes.
Step-by-step explanation:
An egg and sperm are haploid cells which come together in mammalian life cycles in a process called fertilization. Gametes are special cells produced through a type of cell division known as meiosis, where they maintain only half the amount of genetic material compared to regular body cells (diploid cells). In humans, for instance, gametes contain one set of 23 chromosomes.
Fertilization occurs when the male sperm and the female egg cell fuse, thereby creating a zygote. This zygote is diploid, meaning it has two complete sets of chromosomes, one from each parent, and thus contains 46 chromosomes in total. This newly formed zygote will eventually develop into a new individual through a series of mitotic cell divisions and differentiation processes.