GENETICS OF THE BLUE WEIMARANER COAT COLOR
While there are many loci and alleles involved in the Weimaraner’s
coat color (at least 10), there are only two loci that are important
for the blue versus gray coat color in the Weimaraner, the Locus B pair and Locus D
pair. The B genes work in pairs, with one of each of these two
alleles inherited from each parent. The D genes also work this way.
Each of these genes may be dominant or recessive. Dominance is noted
with a capital letter and recessives with a lowercase letter for
that allele. In other words, B is dominant to b, and D is dominant to
d. If present, the dominant gene will determine what you see and
will always “override” the paired recessive.
Locus B Pair
The dominant B produces a black coat color whereas the recessive b
produces a liver or chocolate coat color. Since these genes come in
pairs, a dog could be BB, Bb or bb. BB individuals will be black. bb
individuals will be chocolate. Bb individuals will also be black
because the dominant B “masks” the b. The b is still there and can
and does get passed onto the dog’s offspring, but it is not visible
as the dogs phenotype (the physical characteristic that you can
see). All Gray Weimaraners are bb. Blue Weimaraners are BB or Bb.
Locus D Pair
This pair controls dilution. The dominant D causes full pigmentation
whereas the recessive d produces a dilute pigment. Because D is
dominant, a Dd (or DD) individual will be fully pigmented and there
would be no dilution of coat color. It is commonly accepted
that all Weimaraners are dd; that is, all Weimaraners coats are
diluted and never fully pigmented. Thus, the dd dilution effect
makes the bb chocolate/liver into the light tan that we call
Weimaraner gray, and it makes Bb of BB black into a charcoal colored
dog that we call Blue.
The dilution can work in degrees. In other words, it can make some
dogs lighter than others. Some Blue Weimaraners can be so light as
to appear gray. We must remember that the difference between blue
and gray in Weimaraners is tonal, not the degree of dilution.
Thus a very diluted Blue can be much lighter than a Mouse-Gray, as
can be seen in the top two photos to the right More pictures
of Ellie can be seen on
her website.
When considering inheritance of coat color, we merely need to look
at the locus B pair in Weimaraners since all Weimaraners are dd. A
simple way to determine what a mating would produce is to do a
Punnett square. With this tool we can predict the statistical
outcome of genotype and phenotype. An empty Punnett square looks
like this:
Empty Punnett square
First we would write down the genotype of each parent. Let’s say we
are breeding a homozygous (having the same alleles, so BB) Blue
Weimaraner to a Gray Weimaraner (bb). We would note one parents
alleles on top and the other parents on the side. The empty squares
represent the puppies. Since we know that each puppy inherits one of
the alleles from each parent, we move one allele down into the offspring’s
square.
How we fill in the squares
The completed Punnett square would appear like this:
A completed Punnett square of a monohybrid cross. Gray
Weimaraner bred to a homozygous Blue Weimaraner.
As we can see from the completed Punnett square, a Gray Weimaraner
bred to a homozygous Blue Weimaraner will produce 100% Blue
Weimaraners, and further, all of them will be heterozygous Blues. In
other words, all of the dogs will be blue and carry the gray
recessive.
When we breed a Gray to a Blue who is carrying the recessive b, we
can use the Punnett square to determine that we will statistically
get 50% Blues and 50% Grays:
Gray Weimaraner bred to a heterozygous Blue Weimaraner
Thanks to this simple tool, it is now perfectly understandable how
two Blues can produce Gray pups. Statistically we would see 75%
Blues and 25% Grays:
Two Blues can produce Grays
Punnett squares only help predict probability and results are not
statistically significant when dealing in small numbers. Therefore
it would be theoretically possible for two Blues to produce an all
Gray litter. However because Blue is dominant, it is never possible
for two Grays to produce a single Blue in a litter.
|
