Te overall body plan of the organism is laid down during oogenesis, and in early embryogenesis. In many types of eggs some specific factors (determinants) are symmetrically deposited within these cells what results thereafter in differential mitoses of embryos. The overall body plan of embryo results from a hierarchy and spatially self-limiting activations of fairly universal classes of genes coding some transcription factors essential for pattern formation in different types of embryos, and from activations of genes controlling the geometry of cleavage.