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Hen's teeth (was Re: belated questions about beaks)



 Pat Grant <PATG@vax2.concordia.ca> 
 
> And that got me wondering about those cases where geneticists have
> messed with chicks' suppressed genes, and produced toothy chickens. 
> Are there any published photos or pictures of these creatures?  Might be
> interesting to compare with certain non-avians.

I don't know if the aforementioned experiments proceeded just as you say,
but I'll relate what I have read.

On page 318 of _The Dinosaur Heresies_, Dr. Robert Bakker refers to "recent
surgical manipulation of bird embryos" whereby "experimenters transplanted
tissue from the inner jaw (dental lamina) of an unhatched chick to an area
of the body tissue, where the graft could grow.  In the transplanted
position, the chick's dental lamina started to produce tooth buds!  Birds
with teeth could grow right in the twentieth century."  So the experimental
bird was altered surgically -- not by switching off suppressor genes --
producing tooth buds -- not fully formed teeth -- somewhere on the body --
but not in the beak.  The experiment none-the-less suggests that birds
retain tooth-forming information in the form of unexpressed genes in their
DNA.  Unfortunately, I can find no reference for this experiment at the
back of the book.

I do have references for another experiment which deals with the same
subject:

Kollar, E.J and Fisher, C., "Tooth Induction in Chick Epithelium:
Expression of Quiescent Genes for Enamel Synthesis," _Science_, Vol. 207,
29 February 1980, pp. 993-995.

"Found: Tooth-Making Genes in Chickens," _Science_, Vol. 207, 29 February
1980, p. 149.

In the above experiment, Kollar and Fisher grafted cells from chicken and
mouse embryos into the cavity between the cornea and iris of the eye of an
adult mouse which lacked a thymus gland (in order to avoid rejection of the
foreign tissue).  The resulting molariform tooth, which derived its enamel
from the cells of the chicken, lacks the mammalian cusp pattern, and is
therefore  considered to be somewhat comparable to the smoother teeth of
reptiles.  The articles show detailed saggital cross-sections of the teeth,
but do not provide any long shots depicting the unfortunate mouse.  Here
again, the results of the experiment support the hypothesis for the
persistence of tooth-making genes in the DNA of derived extant birds,
millions of years after the birds lost their teeth, but the experiment does
not provide us with a nice snapshot of a hen with teeth.

Does such a snapshot exist?  Does Stephen J. Gould's _Hen's teeth and
Horses' Toes_ have provide further information?

-- Ralph Miller III     gbabcock@best.com

I've heard (great reference, huh?) that we ourselves share a good deal of
DNA with primitive (extant) bacteria...  Makes me appreciate those
suppressor genes.