Alan,
While I have not kept up with the latest in developmental biology,
but even based on my biology training from the late 70's and early
80's, it seems to be the case that the early stages of development
are controlled factors in the egg itself. Cell division through the
64 cell stage (the blastula) and even the formation of the blastocoel
(the hollow ball of cells just preceding the cell movement of
gastrulation) can occur in the absence of DNA or with DNA replication
chemically blocked. Under normal conditions there is a large amount
of gene expression just prior to gastrulation. However, because of
asymmetry in the egg itself, the cells of the blastula are not all
the same and this can result in further differentiation further down
the developmental pathway even in the absence of gene expression.
One might well wonder at the conclusion that DNA does not program the
development of the embryo. Certainly you can conclude the the
embryo's DNA does not program the initial development of the embryo.
I think there are processes here that don't necessarily involved
direct programming by even the maternal DNA, such as protein-protein
interactions, cell-cell interactions, various forms of self-assembly
and self-organization that occur spatially and temporally apart from
the direct orchestration of even the maternal DNA. However, even some
of the timing of the gene expression and the protein products of gene
expression derive from the maternal DNA--so in that sense it can be
said that DNA programs the development of the embryo.
I really don't believe that Wells is saying anything that most
biologists don't already know. In his effort to get away from a DNA
based development which enhances his attempts to get rid of molecular
phylogenies, I believe that he unwittingly gives additional credence
to self-assembly and self-organization sorts of arguments that
distance some aspects of development from evolution. He turns these
into anti-evolutionary arguments when in reality they just say that
you can't look at *all* developmental processes as being rooted in
some evolutionary history. Some are rooted in principles of
self-assembly, self-organization, morphological restraints, geometric
form, etc. While this is all shocking to some who have been falsely
indoctrinated in the "life is DNA" school, it's been around biology
for some time.
TG
>This is an extract from a website of Jonathan Wells in which he
>describes his calling into the fight against Darwinism:
>http://www.tparents.org/library/unification/talks/wells/DARWIN.htm
>>According to the standard view, the development of an embryo is
>>programmed by its genes-its DNA. Change the genes, and you can
>>change the embryo, even to the point of making a new species. In
>>the movie "Jurassic Park," genetic engineers extract fragments of
>>dinosaur DNA from fossilized mosquitoes, splice them together with
>>DNA from living frogs, then inject the combination into ostrich
>>eggs which had had their own DNA inactivated. In the movie, the
>>injected DNA then re- programmed the ostrich to produce a dinosaur.
>>Experiments similar to this have actually been performed, though
>>not with dinosaur DNA.
>>In every case, if any development occurred at all it followed the
>>pattern of the egg, not the injected foreign DNA. While I was at
>>Berkeley I performed experiments on frog embryos. My experiments
>>focused on a reorganization of the egg cytoplasm after
>>fertilization which causes the embryo to elongate into a tadpole;
>>if I blocked the reorganization, the result was a ball of belly
>>cells; if I induced a second reorganization after the first, I
>>could produce a two-headed tadpole. Yet this reorganization had
>>nothing to do with the egg's DNA, and proceeded quite well even in
>>its absence (though the embryo eventually needed its DNA to supply
>>it with additional proteins).
>>So DNA does not program the development of the embryo.
>
>I know Well carries two PhD's, but this seems just plain wrong. His
>statement that the DNA in an egg does not control the initial
>developement of the embryo seems almost silly. Is he refering to an
>egg with two sets of DNA (one natural one injected) ?
>Any ideas ?
>
>Alan McCarrick
-- _________________ Terry M. Gray, Ph.D., Computer Support Scientist Chemistry Department, Colorado State University Fort Collins, Colorado 80523 grayt@lamar.colostate.edu http://www.chm.colostate.edu/~grayt/ phone: 970-491-7003 fax: 970-491-1801
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