All cells receive different signals during development to differentiate into cell types in the body. When an cleavage of embryo starts which rise to more cells formation, all of the cells are in the same phase of differentiation and receive same signals from their immediate environment.
The embryo is the early developmental stage of an animal whereas it is in the egg or within the uterus of the mother in human.
During further course of development, cells start to get different signals and develop memory to those signals in their DNA (mainly through activation of certain genes). In early stages, embryo's all the cells just work towards establishing what specialised cells they need to become based on their positions in the embryo.
As development follows, memory that is established remains in the cells and guides to further differentiation towards specific roles. The signal that created that memory need not be there.
For more information regarding the cell signaling, visit:
https://brainly.com/question/14407213
#SPJ4