On Sun, 27 Jul 2003 04:11:49 +0000 (UTC), juanpedro.g{at}wanadoo.es (Juan
Pedro) wrote:

>If at the early divisions of a human embryo, the zygote i mean, the
>final destiny of the forming cells is determined by gradients of
>proteins and mRNA in the egg's cytoplasm deposited there before
>fecundation took place, how is it that after a few divisions -let's
>say at eight cells stage- every individual cell still has the power if
>separated of the rest to form a full embyo. The concentrations of the
>above mentioned proteins and mRNA should be different in each cell,
>yet they are totipotent why is it that? Could someone be some kind to
>explain that to me, please? I'll appreciate. (sorry for my awful
>english)

Some types of organism have "determinate" development (more properly,
mosaic embryos) where the fate of each invidividual cell is fixed even
at the first cell division.  Others, like humans, have "indeterminate"
devlopment (regulative embryos) because the fate of the individual
cell is not completely determined until later divisions.  One good web
reference is
http://www.ucalgary.ca/UofC/eduweb/virtualembryo/cell_fate.html

Essentially, the gradients in cytoplasmic factors that you describe
are not yet formed (or not yet sufficiently formed) at the eight cell
stage in humans. They develop starting about this time.

Your English is quite excellent.  mejor que mi espanol!
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