Final answer:
Embryonic development is the complex process that transforms a zygote into a multicellular adult organism, beginning with cleavage and progressing through stages such as the blastula, gastrulation, and organogenesis.
Step-by-step explanation:
The process responsible for the production of the adult body of an animal from a zygote is called embryonic development. Following fertilization, the zygote undergoes numerous rounds of mitosis, forming a multicellular organism. This development begins with cleavage, then progresses to a blastula, followed by gastrulation, and eventually, organogenesis.
During gastrulation, three germ layers form, which are essential for the differentiation into various organs and tissues. This complex series of events ensures the transition from a single-celled zygote into a fully formed multicellular adult animal.