Google Answers: Totipotent cell count in human zygotes: "trophectoderm which produces the chorion and
the cells of the inner cell mass which will give rise to the embryo.
This is the first differentiation event. So, at this point, no cells
are left totipotent. However the ICM cells are pluripotent and able
to form ever cell in the body. the ICM consists of approximately 13
cells by the 64 cell stage."
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