IANBC (I Am Not Bob C), but this is too much fun for me to resist.  Bob's
answer will be even longer than mine, since I only have a single weak copy
of the lecture gene, but it's still probably as long as you can stand.  B-)
 
Regina J. Hart" <ferret@u...> wrote:
>In light of your discussion regarding depigmentation, is it possible for
>a ferret to express a depigmented pattern (e.g.  blaze, mitt, panda, bib,
>etc.) without the presence of the Star Gene and/or Waardenburg's Syndrome?
 
Sure.  But that doesn't mean that the resulting depigmentation isn't
associated with problems.  There are lots of genes involved in the
development, structure and functioning of pigment cells, and any one of
them could have one or more alleles that result in some degree of
depigmentation.  Since many (maybe even most) genes affect more than one
trait, an allele that causes depigmentation is likely to have other
effects.
 
White patterns associated with deafness are NOT always caused by the genes
associated with Waardenburg's Syndrome (WS).  There are five genes that
are implicated in the different types of WS.  These genes are called PAX3,
MITF, EDNRB, EDN3 and SOX10.  However, most white markings in domestic
animals appear to be related to the KIT gene, which is often referred to
as the "S" ("spotting") locus in discussions of coat-color genetics.  White
markings caused by alleles of this gene are also associated with deafness,
and can range from forehead markings to extreme piebald patterns.  For
example, this is the gene that is responsible for the coat pattern of
Dalmatian dogs, as well as the high incidence of deafness in that breed.
(Question: has anyone actually SHOWN that deaf ferrets with white markings
are usually suffering from WS, or have we just been going along with an
assumption somebody once made?  My guess is that we've been using the term
far too casually, and that the KIT gene is largely responsible for blazes,
pandas, etc.)
 
More about problems related to white markings below.  But, first it's
interesting to ask if there exist any genetic mechanisms that can cause
depigmentation with NO associated problems.  My guess on this would be
yes.  There are a number of species that appear to exhibit some type of
depigmentation, but certainly aren't domesticated (no Star gene): skunks
have stripes, badgers have blazes, zebras are striped, and panda bears
are ... well ... panda.  It seems unlikely that these patterns would
persist in the wild if they were associated with some detrimental condition
such as deafness, which means that the underlying genetic causes are
probably different than the common causes of depigmentation in domestic
animals.  (OTOH, it is possible that these species derive so much survival
benefit from their coloration that it more than makes up for a certain
percentage of defective offspring.  Somehow I find this hard to believe,
though.)
 
So, why aren't these "safe" depigmentation genes working in our domestic
animals?  Darned if I know.  They aren't all that common in the wild, so
maybe we just need to wait a couple million years for the right mutation to
show up.  Or, maybe they *are* here, but we just can't tell.  For example,
if I have two panda ferrets that aren't deaf, how would I know if one was a
mild case of WS while the other has some "safe" genotype?  Someday maybe
there will be a Ferret Genome Project and we will then have genetic tests
that can tell the difference.
 
(I should also note that there is a difference between "depigmented" and
"white".  If the hair is white but the skin can produce pigment, then the
animal is not depigmented.  For example, Samoyed dogs are depigmented, but
polar bears are not, having black skin.)
 
>In addition to auditory and visual problems, what -if any- other problems
>are documented in Star Gene and/or Waardenburg's Syndrome individuals?
 
There are a zillion problems (scientifically speaking B-) associated with
various types of depigmentation.  Failure of the neural tube to close,
cleft palate, enlarged colon, anemia, infertility, behavioral disorders,
reduced intelligence, limb malformations, problems with balance, etc.  It
all depends on which gene or genes are causing the depigmentation.
 
There are some interesting aspects to hearing problems associated with
white markings, especially where the KIT gene is involved.  For example,
I mentioned that this gene is involved with both spotting and deafness in
Dalmatians.  However, the incidence of hearing loss in Dalmatians with
black patches on the ears is much lower.  The KIT gene is also responsible
for the white head, belly, feet and tail switch of Hereford cattle, yet
I've never heard that deafness is a particular problem for this breed.
Note that Herefords have pigmented ears.  While I don't know what genes are
responsible for the markings of panda bears, I do note that they, also,
have pigmented ears.  This seems to indicate that genotypes exist that
allow pigment cells to migrate to the ear during embryonic development --
resulting in normal hearing -- while restricting migration to the skin and
coat sufficiently to produce the white markings that many find desirable.
Unfortunately, we don't yet know how this works, though it probably
involves some modifier gene(s) that interact with the KIT gene.  We also
don't know if ferrets are one of the species in which this could be
accomplished.  (We also don't know how far we could go in eliminating
deafness in Dalmatians.  Patches are considered a disqualification in the
Dalmatian breed standard!  Talk about shooting yourself in the foot ...)
 
Behavioral problems associated with depigmentation are another interesting
phenomenon, and are related to all types of depigmentation (such as
albinism), not just those types caused by a lack of pigment cells.  For
example, albino mice are known to be much more "emotional" or "reactive"
than pigmented mice.  Viennese white rabbits are subject to seizures.
Pointer dogs suffering from the "nervous behavior" defect tend to be highly
depigmented.  Holstein cows with large amounts of white are more nervous
and less productive.  White pigs are more likely to suffer from Porcine
Stress Syndrome, which kills them when they are subjected to stress or
exertion.  (It would be interesting to know just how many of these
phenomena are directly related to reduced auditory and/or visual acuity.
For example, I don't think anyone ever bothered to check those nervous
white Holstein cows to see if they were hard of hearing or had bad
eyesight.  We certainly know that deaf ferrets require special handling
to avoid provoking fear and aggression.)
 
>OK, make that three - What is your personal opinion with regard to the
>breeding of these individuals?
 
I, myself, would not.  As I see it, there are only two other choices:
breed them without regard for health (not very ethical), or embark on a
full-scale program to develop healthy strains of marked ferrets (which
would involve large amounts of inbreeding and ruthless culling, with all
the attendant heartbreak).  All for the sake of a characteristic that is
of no particular benefit to the animals or the species.  Look at all the
horrible things that have been done to so many breeds of dog, cat and
livestock -- all resulting from breeding programs that treat animals as
some kind of artwork to be molded according to some abstract esthetic
standard divorced from any concept of biological reality.
 
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
 
>While I'm directing these questions specifically at Bob, I'd be really
>interested in hearing from anyone who can provide insight!
 
I'd like to hear what Bob thinks of the idea that H. Sapiens actually
qualifies as a domestic animal!  We may very well have domesticated
ourselves before we started on the others.  B-)
 
--
Brett Middleton
University of Georgia
[Posted in FML issue 3406]