What is the sequence of development from zygote to the stage where differentiation begins in humans?

The development sequence in humans begins with the formation of a zygote, which is the fertilized egg resulting from the union of sperm and egg. Following this, the zygote undergoes several rounds of cell division, leading to the formation of a morula, which is a solid ball of approximately 16 to 32 cells.

This early stage is characterized by cleavage, the rapid division of cells without growth, which helps to increase the number of cells in a compact form. After the morula stage, the cells start to differentiate and organize themselves into a blastocyst, which includes an inner cell mass (that will eventually form the embryo) and an outer cell layer (the trophoblast, which will form part of the placenta).

The key point here is that differentiation begins as the development progresses from the morula to the blastocyst stage, where the inner cell mass is formed. Thus, the transition from zygote to morula accurately represents the sequence leading to the initial stages of differentiation in human development.