What process occurs after fertilization of the egg and sperm to produce a multicellular organism?

After fertilization occurs, the zygote undergoes a series of developmental processes that lead to the formation of a multicellular organism. Mitosis is the key process in this stage. It is a type of cell division that results in two daughter cells that are genetically identical to the parent cell. The zygote divides through mitosis, increasing the number of cells and gradually forming an embryo. This process continues as the cells divide and multiply, leading to the development of various tissues and organ systems in the organism.

While other processes, like apoptosis or differentiation, do occur during development, they play different roles in the life cycle of an organism. Differentiation refers specifically to the process by which cells become specialized for specific functions, while apoptosis is the programmed cell death that helps shape and regulate the development, particularly in removing unneeded cells. Meiosis, on the other hand, is the process that generates gametes (sperm and egg cells) and is not involved in the post-fertilization development of a multicellular organism.