|Without differentitation cells would divide
and just end up as a clump of cells. Instead, as cells divide they
get different sets of instructions. This occurs very early in cell
It starts with the single cell dividing.
early cleavage click
Division stops when a pre-determined number
of cells are reached.
At a certain point during the early cell
divisions genes are turned on in certain cells, but not in others, while
different genes turn on in other cells.
These cells are now destined to become
different from each other that will each serve different purposes.
As groups of cells differentiate and undergo
cell division they MIGRATE (move) to a different areas of the embryo.
Gastrulation click here
Sea urchin click here
As they continue to differentiate they
begin to now "LOOK" different and form
i. Structures like the backbone,
ii. Organs like liver,
iii. Eye sockets and eyes,
iv. The mouth, etc. ...
g. All of this occurs in a PRECISE SEQUENCE.
Complete Xenopus development
As additional groups of genes are turned
on and off and further differentiation occurs, the morphology is changed
yet again, cells and structures molded by the genetic program until the
stage at which the species of the embryo is clearly set.
Even after external morphology is set,
further differentiation occurs internally.