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MERLE SMALL DOGS IN
"Genetics, whether of the dog or Homo sapiens, is never
a simple subject that can be simply explained." (Onstott 1978;ix)
Even a cursory examination of the substantial body of
research reported in the literature would indicate, however, that the
decision to not introduce the merle modifier into the chihuahua gene
pool in
GENETICALLY MODIFIED
The merle gene is in fact a modifying gene (Whitney 1971;192), that is, it
genetically alters and lightens dark coloured coats as well as the pigment in
the iris of the eye and the middle ear (Lambert 2004).
GM chihuahuas! While there is considerable uncertainty
about the ramifications of genetically modifying foods, there is ample
scientific evidence of the dire consequences of the merle gene in dogs.
MERLE
Whitney (1971;194) states that to his knowledge, there is no
solid white in dogs. Whites include the albino white, the dark-eyed white
and the common white associated with spotting. Whitney (ibid;204)
continues "There is one other white which is definitely different from the
others so far discussed. It is found in Norwegian harriers and in
collies, both rough and smooth, and in shetland sheepdogs. This is a
white of a semi-lethal
nature. When one of these is crossed with a black-and-tan or tricolour, a
curious colour called 'merle' is produced. This white, which almost
invariably weakens the possessor, is a very undesirable character ..."
DEAFNESS
Willis (1989;275) reports that the association of merle
colouration and deafness is well established. In the homozygous state,
the M allele causes rough and smooth collies to be almost white and research
has shown that such dogs are usually deaf and have eye defects.
Dr George Strain, Professor of Neuroscience Comparative
Biomedical Sciences, Louisiana State University of Veterinary Medicine (2004)
states that dogs with blue eyes are 50% more likely to be deaf than are dogs
with brown or black eyes.
EYE DEFECTS
In the dachshund breed, the M allele leads to
dappling. The
STERILITY
As well as identifying eye and ear problems, the Hanover
research revealed impairment of sperm production in both MM and Mm dogs
(ibid;275).
MERLE TO MERLE
Onstott (1978;237) found that "Merle to merle yields
50% of the progeny merle, 25% black and 25% white. The whites will be
both deaf and blind."
Some breeders claim that as long as merle is not
bred to merle, no genetic problems can occur.
Willis, quoted above, is quite categorical, however, in
stating that Mm cases DO suffer ear and eye defects similar to those in
the merle to merle (MM) matings. So where a dominant M is mated to a
recessive m (Mm), which recessive we might not even know about, problems
DO occur.
A further complication is that Whitney (1971;139) found coat
colour modifiers (such as merle) can be dominant but not show. Willis
(1989;70) agrees that some dogs may not even be identified as merles even
though genetically they are.
Thus, it is not possible to be absolutely certain that one
is NOT breeding merle to merle.
WHERE DID THIS MERLE PATTERNING IN THE
Lambert (2004) established that the rapidity with which
merle chihuahuas appeared is highly unlikely to be due to a single
mutation. On ascertaining that the breeders of the first merle chihuahuas
also had dachshunds, her group emailed those breeders. They received not
one response.
Dr Strain (2004) confirms "It seems highly
unlikely that a NEW spontaneous mutation in the recessive allele in your breed
would produce the same phenotype of the dominant allele. I could not say
this as an absolute but in my opinion the merle has to have been introduced
from another breed. Because the merle pattern is dominant, it could not
have lain 'silent' for many generations only to reappear fairly recently."
Yes, the merle chihuahua has to be a
cross-breed. So in addition to the still-experienced pomeranian small
erect-carried ears, slightly oval eyes, slightly flat skull and harsh coat, or
papillon colouring, nose, eyes and butterfly ears, chihuahua
breeders would have dachshund-like or sheltie-like features with
which to contend. Certainly, some of the small merle dogs appearing on
various websites have decidedly dachshund-ish or sheltie-ish heads with
long noses and almond shaped eyes.
A local veterinarian has recently brought to my notice that
a larger merle dog such as a dachshund, sheltie or Aussie
shepherd crossed with the chihuahua will result in heavier bone. He
believes that this additional weight is highly likely to be detrimental to the
stability of particularly patellae, but also other joints, in
our breed.
A further issue is the possible appearance of blue (light)
eyes in dark coloured chihuahuas which is not permitted by the breed
standard.
GETTING RID OF DEFECTS - AND UNDESIRABLE CHARACTERISTICS
Willis (1989;298) concludes that we can never totally
eliminate defects. The rarer an allele becomes, the more difficult it is
to reduce it still further so that a breeder's very success early in his
breeding programme makes progress harder and slower in later years.
He further states "Very rare defects, like some
lethals, will be hidden for years, may not even be known about, and then will
come to the surface under an inbreeding progamme." (ibid;327)
Even with the most judicious of breeding, most of us have
witnessed the sudden and unwelcome appearance of defects and undesirable
characteristics we thought we had eliminated - or, indeed, we didn't even know
about.
Do chihuahua breeders in
Certainly, the Germans do not and have banned the merle
chihuahua (Lambert 2004) while Italy has banned both the merle cardigan corgi
and the merle collie.
The opinion of the Hanover Veterinary School researchers
that breeding with the merle factor should be restricted to scientific purposes
has already been cited above.
Harmer (1975;9) agrees "... it would be better for
merle to be a disqualified colour in all breeds."
Australian chihuahua breeders can do no better
than to heed Stockman's (1990;44) advice, "Dog breeding is a
tremendous challenge and can be enormously rewarding as a hobby. But
there is no place for the irresponsible ... think before you mate ...".
REFERENCES :
Harmer, Hilary "Dogs and How to Breed Them" John
Gifford Ltd 1975
Lambert, Gloria "Merles" unpublished paper 2004
Onstott, Kyle revised by Philip Onstott "The New Art of
Breeding Better Dogs" Howell Book House Inc. 1978
Stockman, Mike in Trevor Turner Ed. "Veterinary Notes
for Dog Owners" Popular Dogs 1990
Strain G. in Gloria Lambert "Merles" unpublished
paper 2004
Willis, Malcolm B. "Genetics of the Dog" HF &
G Witherby Ltd 1989
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