What crucial developmental process occurs during gastrulation?

Gastrulation is a fundamental phase in embryonic development that is primarily characterized by the formation of individual tissue layers. During this process, cells move and reorganize to establish the three germ layers: the ectoderm, mesoderm, and endoderm. Each of these layers will ultimately give rise to different tissues and organs in the developing organism. The ectoderm typically forms structures such as the skin and nervous system, the mesoderm contributes to muscle, bone, and circulatory systems, while the endoderm forms internal linings and organs like the digestive tract.

The other processes listed, such as DNA replication, division of the zygote, and protein synthesis, are important in cell biology and development but occur at different stages or serve different functions. For example, DNA replication is crucial for cell division but happens prior to and during cell cycle phases, not specifically during gastrulation. The division of the zygote occurs earlier and lays the groundwork for subsequent developmental stages, while protein synthesis for cell growth is a continual process that supports various functions throughout development. Consequently, the primary event that defines and occurs during gastrulation is indeed the formation of individual tissue layers.