Cleavage is the rapid mitotic cell divisions that immediately follow fertilization. As the number of cells increases to about 16 - 64, the embryo is called a morula. Cleavage does not increase the size of the embryo. Thus, the cells become smaller as their number increases.
All cells in a morula look similar. However, they may contain different cytoplasmic materials due to cytoplasm rearrangement. These subtle differences are important for subsequent cell differentiation.