Biology Reference
In-Depth Information
A
A'
random
events
c
b
c
b
B
C
mutual
selection
(adapted from Kupiec, 1983, 1997)
F IGURE 20. The Darwinian model of cell differentiation. The cells A and A′
differentiate into B or C depending on the random molecular interactions b or c which
are produced. Cellular interactions are also involved in the selection or stabilisation
of these randomly obtained phenotypes.
depending on which set is expressed, the cells differentiate into
type B or C.
Interactions between cells do occur in this model, but their
function is not to induce their differentiation as is the case in the
instructive model. They select or stabilise the cells which differen-
tiate randomly. In Fig. 20, the interaction between cells B and C
leads to selection (or stabilisation) of B by C and of C by B, and
therefore to their coordinated differentiation.
Unlike the instructive model, in the Darwinian model the pre-
cision of embryonic development is not based on the precision of
molecular events, as prescribed by the principle of order from
order. Two factors play complementary roles. Firstly, there is a
population effect. While random events cannot be reproduced in
the cell or the individual molecule, they are reproduced, statisti-
cally, in cell or molecular populations, in which they do so with sta-
ble mean frequencies subject to variations depending on the size of
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