I was rereading the post and realized my answer for the hybridization
part was a bit terse.
 
The thing you have to realize is that ferrets were domesticated to do
exactly the same things polecats did, ONLY to be more manageable by humans.
Do do that, you simply breed out fearfulness, which, coincidentally breeds
in domestication.  But there is an important implication as well, and it
is that ferrets did not change much in terms of their body structure, fur
color, and size or proportions.  What changed was the BEHAVIOR of the
animal.  That doesn't make the ferret any less domesticated than the dog;
even the cat has undergone relatively few external or physiological
changes in 3600 years.  All it means is that it defines most causes of
domestication; that is, behavioral changes.  Now, don't feel dumb if this
is hard to understand or easy to miss, because Darwin missed it as well,
classifying the ferret as "semi-domesticated" because of the lack of
external changes.  (<sigh> My heroes are only human...)
 
So, when I argue that polecat hybridization with ferrets doesn't cause
external changes, but DOES cause behavioral ones, it is based on the
knowledge that the allelic frequencies coding for behavior are quite
different between polecats and ferrets, but the allelic frequencies
governing external morphology and physiology are quite similar.  Many
recent studies show most of the changes in physiology and morphology
between domesticates and their progenitors are due to timing changes
during fetal development, NOT in genetic changes to the genes governing
physiological or morphological processes (it is very complicated,
involves polygene interactions, neurochemicals and hormones, and is not
fully understood).  Strangely, breeding for tameness also causes a change
in development, resulting in a juvenilization (or neotony) of the animal.
And that is what is confusing when you breed a polecat to a ferret.  You
think you have achieved a darker black or more muscles, but there has been
no change in those genes, only in their expression.
 
Here's an example.  Domesticated animals are generally lighter in color
than their progenitors, especially in the blacks, which typically turn
to a dark brown under initial domestication.  But there may be no change
in the actual color genetics of the animal.  One of the changes caused by
domestication is when the embryo is initially developing, and pigmented
cells are migrating to the skin.  The timing of the migration is subtlety
disrupted, so cells which would result in black fur now only produce dark
brown.  This timing disruption is also thought to result in those white
patches you see on the foreheads of so many domesticated animals, including
dogs, cats, pigs, cattle, horses, ferrets, bunnies and rats.  In other
words, domestication doesn't change the genes to stop coding for black
and to start coding for brown, what it does is change the expression of
the same gene so black only expressed as brown.
 
Why?  Because when you select for behavior to increase tameness, you
accidentally tap into the animal's development center.  That is why neotony
is a universal trait of domestication.  But you also get a tame, fearless
animal.  Which brings you back to the hybridization issue.  If the major
selective change in ferrets was for behavior, what happens when you cross a
ferret with a polecat?  You get a change in behavior, maybe not as positive
as you might think.  The problem is, the changes in morphology are not so
much due to the introduction of new genes, but in the expression of the old
ones.  Because the timing differences which make the ferret domesticated
influence the expression of many physical traits, many times when you think
you have introduced a new gene, all you have actually done is change the
expression of an old one.  The problem is, with domesticated ferrets,
that can only mean you have lost the traits of domestication, namely
fearlessness.  The resulting offspring are usually not well suited for
children or most adults.
 
The bottom line is, crossing ferrets to polecats in the hope of finding
a new gene, or to help eliminate a bad one, actually results in behavior
changes of a potentially profound nature, and at the receiving end of many
a mink and weasel bite, I can confirm the action is potentially dangerous.
If bad genes exist in a population, the easiest way to get rid of them is
not to breed the traits in; simply neuter than animals and it is the same
effect as killing them (reproductive culling).  Those genes will never
splash in the gene pool.  If you want new traits, you have to do it the old
fashioned way, which is careful and selective breeding, detailed breeding
records, and the realization that it ultimately depends on a favorable
mutation which can be conserved and passed on to future offspring (like
long fur on angora ferrets).  But your chances of getting those types of
traits from polecats is somewhere between "nil" and "slim".  All you will
do is breed a less trustworthy, less dependable animal, which harms all
of us.
 
Bob C and 15 Mo' Melano-Mistakes
[Posted in FML issue 3251]