"Variable Expression" is one way to refer to a genetic situation having a
range in degree of results.  Yes, Waardensburg has variable expression, so
some may have no hearing loss (but might still have offspring who do), or
compromised hearing, or full deafness.
 
As long as we are speaking of breeding and traits which may be indicators
that a line is less viable (whether less viable for survival, or harder to
train, or whatever...) it might make sense to discuss other things which
could be POSSIBLE INDICATORS (Read as not necessarily but check with a good
vet to be safe.) of some other problems.  I know folks here will know of
ones with which I'm not familiar.
 
One which happens in humans and some other mammals (Do NOT know if it is
a problem in ferrets.) is that aortic arch alterations can exist in some
individuals who have eye colors or fur colors which are NOT bilateral
(matching on both sides) so a breeder seeing that sort of thing would want
to hold back the line and monitor the health extra carefully for several
generations.
 
A face which is too short can result in a number of discomforts for the
ferret.
 
Fur which remains lush and kitlike throughout life may be associated at
times which acondroplasic dwarfism, which can be very uncomfortable and
carry special health concerns.
 
Hey, I am just writing this as someone who worked for years to help Ruffle
who lived to be 6 -- though no one expected her to make it so long -- and
who died of having multiple growths, lesions, cysts, and cardiomyopathy
happen at once, had very shortened and arthritic limbs, very large and
non-flexible trunk, very short face, incredibly long and lushly thick fur,
asthma, clinical retardation, altered mobility from the norm, multiple soft
tissue deformites, abnormal spine, etc.  (Bob can verify how unusual her
skeleton was; he once used the term "on the edge of survivability" which
combined with "non-viable" and "failure to thrive" were terms we also heard
from vets, a veterinary pathologist, and consulting vets over her 6 years.)
When she was a kit her breeders were really happy to get kits with
shortened malamute-like faces (drop dead gorgeous) and luxuriant fur
(ditto), not realizing the price those came with at first.
 
Basically WHENEVER a breeder winds up with a line which looks or acts a
good bit different from the norms it really pays to monitor those lines
very carefully for several generations to be sure of what you have, and
this is also true when you have gotten something you had been trying to get
such as dramatic fur.
 
Sukie
[Posted in FML issue 2580]