I’ve been told that the unfertilized egg contains cytoplasmic determinants (e.g. proteins, transcription factors, mRNAs) that are divided unevenly during the early stages of cell division in an embryo. Thus, each embryonic cell has a different cytoplasmic composition with a different set of transcription activators, allowing the expression of only certain genes.
By this token, it seems to me that this uneven partitioning of cytoplasmic determinants occurs in the very first division of the zygote. Thus, the first blastomeres are already no longer totipotent. Is that correct?