Therefore it contains a special set of proteins, mRNAs etc. to trigger development. As cells of embryo specialize, most of the cells will turn off the genes that will never be needed again. So fate of each cell becomes progressively restricted as it gets more and more specialized. B. Cells must do all of the above without changing their DNA . Therefore all DNA in all cells of plant must be functional.
Regeneration shows some specialized cells can switch fates.
Which genes are transcribed must change, not the genes. 2nd messengers, cascades, etc. Position of determinants sets fate of cells in that part of the egg. After cleavage, different cells have different concentrations of cytoplasmic determinants, morphogens, etc. Different TF genes turned on in dif.