Re: Reverse-engineering the T. rex genome

["Phillip Bigelow" <bigelowp@juno.com>]

Tim Williams <tijawi@yahoo.com> writes:


<<As a gene person, I really hate to derail your train of thought, but the 
susceptibility of the host to this infection has much more to do with the 
properties of the parasite than it does to the host's genome.  Certainly, there 
is something about the theropod/avian physiology that renders them susceptible 
to this kind of parasite.  But the infection proceeds not because certain host 
genes are absent (or turned "off").  The infection sets in because the parasite 
has the ability to overcome the immune response and other defenses of the 
host.>>


Apparently, for crocs and gators, the immune response (and other defenses) 
defeat the microorganism (otherwise the disease wouldn't be characterized as an 
"avian" disease.

Maybe I'm bogging myself down in semantics, but isn't the animal's unique 
immune response (or lack there-of), and its other unique defenses to infection 
(or lack there-of) predisposed by its genes?

If it isn't predisposed by genes, then why do only birds get this infection?


Digging my hole deeper,
<pb>
--









  It is the attempts by the host's immune system to deal with the infection 
that causes the debilitating symptoms (as stated in the paper).

It is true that the properties of the host are important.  To use _Homo 
sapiens_ as an example, when flu season comes along not all of us catch the 
flu, despite being exposed to the disease-causing agent (a virus, in this 
case).  However, the agent can only survive inside a host because it has the 
ability to resist the host's defenses (at least for a time), and replicate. 

BTW, the infection in question (trichomonosis) is not bacterial, but caused by 
a flagellated 'protist'.

 
> Whatever the cause, it IS genetic (what else could it be?),
> and it is shared between at least T. rex and birds.

No, it is not genetic.  The term 'genetic' explicitly refers to the process of 
inheritance.  Even vertical transmission (such as from parent bird to nestling) 
is not 'genetic'.


> A segment of genetic material (nuclear or mtChondrial),
> related to this disease, is shared between birds and T.
> rex.  When researchers pin-point the segment, then they
> have also discovered (unwittingly?) a segment of T. rex
> genetic material,  even though they don't have a
> physical sample of the gene(s) in their hands.


I would say that the protist responsible for infecting _T. rex_ may  share 
genes with _Trichomonas gallinae_ which are responsible for the infection.  It 
is these genes, carried by the parasite's genome, that are most important in 
pathogenesis.


Cheers

Tim


      


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