There seems to be a feeling among some out there that all genetics
follows one pattern for how and when a characteristic is expressed.
 
Genetics is marvelously complex.  There are genetic changes that alter
early fetal cells that themselves lead to multiple later types of cells
so the expression in those cases is variable (as with neural crest
genetics).  There are cases of simple dominance and others of blending.
There are ones where the result of combining two different alleles
results in features that go beyond either of the two alone (for instance
situations in which the offspring may be substantially larger than either
parent.  There are effects of the alleles in different locations on
expression.  There are ones which are safe or even more healthy in single
copies but very dangerous in double copies (the example that is often
used is the allele for Sickle Cell which protects against malaria in one
copy but causes Sickle Cell Anemia in double copies.  The list goes on
and on.  Classical Genetics has documented some marvelous interactions,
which show themselves in a wide range of ways.  There is no reason to
pretend that it all can be explained in one way.
 
As to in-breeding.  If a person could be sure that the individuals didn't
have such hidden bombs as alleles that are fine in one copy but dangerous
in two copies, and so on then it could be fine, but you find me even one
person here who claims to be able to tell you the particulars of all of
the thousands of alleles any individual ferret has and I'll show you a
liar.
 
So, why take the risk?  It's like Classical Geneticist, Dr. Brett
Middleton has said in relation to people who unwittingly breed ferrets
with neural crest genetic variants (like blazes or pandas):
 
>The responsibility of breeders to consider the well-being of the animal
>in their selection programs is an aspect of animal welfare that is too
>often neglected.  Too many people who would never consider beating or
>starving their animals suddenly seem to lose all sense of ethical limits
>when it comes to breeding them.  Temple Grandin at Colorado State
>University has written quite a bit on this subject, and her articles are
>well worth the time to read.  I recommend the following two for starters:
>
> http://www.grandin.com/welfare/genetics.animal.welfare.html
> http://www.grandin.com/references/horse.genetics.html
 
See:
http://fhl.sonic-weasel.org/browse.php?msg=YG3069
 
-- Sukie (not a vet)
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[Posted in FML issue 4960]