[pyrnet] Not so simple recessive...

[Patric Lundberg <pyrsrgr8@yahoo.com>]

Joe,

> Could a simple recessive problem 'sometimes' be accompanied by a poly
> genetic problem that would account for such observations?

Sure.  Anything is possible, but until we have a physical means of
determining exactly what is wrong in any given animal, all we can do is
to take whatever data we have and model onto it a genetic scenario that
fits.  Complicating this issue is of course the level at which any
given change in a gene actually results in a phenotyic change that we
can say (by just looking at the dog and maybe its Xrays): 'This *is* a
dwarf.'

{I now apologize in advance for some tech-talk below.
 I will try my best to make it digestible...}


Take this example for instance (no need for a modifier locus):

The causative gene is a receptor on a cell.  Normally, this receptor is
contacted by its signalling molecule during development and the system
really only works in bone tissue; its function is to stop bone growth.

This seems simple - alter the receptor and you might get a dwarf,
right?

Well, consider this...

1.  The genetic alteration (GA from now on) causing the dwarf phenotype
is one that makes the receptor always be in an "ON" state - bone growth
is stopped too early during development.

2.  A second GA could compensate for the change in 1., either
completely or partially, resulting a slightly early shut-down the
receptor.

3.  Other GAs give mild signalling excess, somewhat like "a partial
dwarf" - Xrays may be conclusive, but you would need a really trained
eye to visually pick it up, so most of these guys are never Xrayed...

4.  All the above might also apply to the signalling molecule, or
necessary gene expressed in the cell that makes it, or another gene
product entirely that is crucial for the signalling pathway the
receptor engages.

So, in conclusion, there is no answer until we have The Answer...

Later, Patric.



=====
"Sage Advice Improves with Thyme"

Patric Lundberg, PhD
patric@pyrealm.com
Department of Virology
City of Hope National Medical Center
(626)359-8111 x2612

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