Final answer:
In early embryonic development, cell divisions occur without the G1 phases and activation of embryonic genes, utilizing a modified cell cycle for rapid growth.
Step-by-step explanation:
Cell divisions in the early embryo follow a modified cell cycle with no G1 phases and no activation of embryonic genes. During early embryonic development, cells divide rapidly in a process known as cleavage cell divisions, which is marked by a shortened cell cycle. Unlike the typical cell cycle, these early cell divisions bypass the G1 phase, which is normally a period of cell growth and preparation for DNA replication, and the G2 phase, which is a checkpoint and preparation for mitosis.
Additionally, during these early stages, the transcription of the embryonic genome is largely inactive, meaning there is no activation of embryonic genes. Instead, the embryo utilizes maternal mRNA and proteins already present in the egg. This streamlined process allows for rapid cell division needed to form the multicellular structure of the embryo.