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Dewclaws are actually rudimentary thumbs
and rear dewclaws are residual fixtures from the past. They have no function and
are situated high on the inside of the leg above the foot. They do not make
contact with the ground but are said to brush the dew from the grass and it is
thought that this is where they get their name. They are called "Wolf-claws" in
Europe but since the Wolf normally has no more or less toes than the dog it
seems strange and unjustifiable to attribute the name back to the
wolf.
Dewclaws may be Bilateral or Unilateral
although most breeds seem to have bilateral front dewclaws. Rear dewclaws are
not as common and are often removed from infant pups when they are
present.
Sometimes there is only a vestige of the
extra toe and it may be just in the skin or under it. Some Geneticists say
dewclaws are Dominant and some say they are Recessive. This conflict does not
alter the fact that the dewclaw represents a fifth toe, which is, through some
evolutionary process no longer needed. There are some very good arguments for
removing them from the rear legs as they can interfere with movement. Whether
front or rear they can catch on things and even on each other and lock in a
"handcuff" situation, causing a bad fall, fractures, and tearing of the skin
surrounding the toe. Chihuahuas often injure their eyes with the front dewclaw
when they use their front paws to clean their faces and eyes.
Because the mode of inheritance is still
unclear and seems to behave differently in certain breeds it is accepted that
dewclaws are Dominant Recessive with Incomplete Penetrance. They are definitely
autosomal which means they can be passed on to either sex.
More confusing yet interesting facts are
that, double dewclaws are recessive to single ones, dogs can carry both genes
and that those genes can act independently of each other. This means that we can
see parents without dewclaws produce pups with 1 or 2 or 1 double and 1 single
or none at all.
Although they are usually removed within a
few days of birth if the breeding records show that two pups were born with rear
dewclaws, when mated together the pair may never produce them or may produce any
of the combinations demonstrated above.
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