|
Pam Crump Shih
Tzu |
|
|
Breeding for Rare
Colors |
AKC
recognizes for the Shih Tzu two pigment colors that come from recessive genes:
Blue and Liver
Genetically,
a Shih Tzu can exhibit both Blue and Liver. In
this case, the pigment takes on a slight purple hue, which has been referred to
by breeders as Lavender. AKC does not yet provide a color for this
condition, so breeders generally will register this as Liver.
Breeders
will often refer to the Liver color as Chocolate, which sounds more
appealing than Liver.
Also the
tan markings (that are located similarly to the markings of a Doberman Pinscher) come from recessive genes. This marking is referred to by breeders as
the “Dobie” marking.
These
colors and marking are relatively rare since they come from recessive genes,
meaning that both parents of a puppy must “carry” that recessive gene for the
puppy to exhibit that color or marking.
The
color of the hair is not crucial to
classifying a dog as Blue or Liver color.
Rather, the determining factor is the color of the “points” (eyes, nose,
lips, paw pads).
If these features are Liver rather than Black then the dog is classified as Liver. If these features are Blue, then the dog is classified as
Blue.
Conversely, if these features are Black, then the dog is neither Blue nor Liver even if the hair appears
to be Blue
or Liver.
One of
the breeding objectives of some breeders is to produce the rare colors and
marking, since there is generally more demand than supply. Knowledge of color genetics is vital to
success in these breeding plans. The
following summary should give a working understanding of recessive gene
genetics.
For this
analysis, all Shih Tzu will be classified as to color (or marking) as one of
the following:
1.
Recessive COLOR
(and thus a recessive gene carrier)
2.
Recessive gene
CARRIER (but not a recessive color)
3.
Recessive gene
NON-CARRIER (and thus not a recessive color)
All
possible combinations of two parents are presented in the table below, which
shows the recessive gene results of the breeding.
|
Parent # 1 |
Parent # 2 |
Puppies |
|
|
COLOR |
COLOR |
COLOR |
100 % |
|
COLOR |
CARRIER |
COLOR CARRIER |
50 % 50 % |
|
COLOR |
NON-CARRIER |
CARRIER |
100 % |
|
CARRIER |
CARRIER |
COLOR CARRIER NON-CARRIER |
25 % 50 % 25 % |
|
CARRIER |
NON-CARRIER |
CARRIER NON-CARRIER |
50 % 50 % |
|
NON-CARRIER |
NON-CARRIER |
NON-CARRIER |
100 % |
DNA
Testing Source: DDC Veterinary website at
B Locus
(DNA markers tested – S41C, P345Pel, Q331X)
Associated
with the presence of chocolate (also commonly referred to as liver or brown).
The bb genotype usually results in a chocolate coat phenotype and liver noses
among yellow dogs.
Possible Genotypes:
BB – does not carry brown
Bb – brown carrier
Bb2 – brown carrier
bb – brown
phenotype [This value is necessary to exhibit Liver]
D Locus
(DNA marker tested – C.22G>A)
Associated
with the dilution or lightening effect of solid colors, with D being the
dominant allele, the dd genotype results in the
diluted effect (like grey, blue, silver, lilac,
champagne).
Possible Genotypes:
DD – does not carry dilute
Dd – dilute
carrier
dd
– dilute phenotype [This value is necessary to
exhibit Blue]
To
exhibit Lavender
both the B Locus must be
bb and the D Locus must be dd.
at Locus
(DNA marker – ASIP reference: Schmutz S and DL Dreger. A SINE Insertion Causes
the Black-and-Tan and Saddle Tan Phenotypes in Domestic Dogs. Journal of
Heredity 2011, 102(S1):S11-S18.)
This
color allele is associated with generating the commonly known phenotypes known
as “tan points”, “phantom” and “tri-color” among several breeds. The inheritance
and expression can vary depending on the breed.
Possible Genotypes:
awaw – 2 copies of the non-tan
point allele
awat – 1 copy of the non-tan point
allele and 1 copy of the tan point allele
atat
– 2 copies of the tan point allele [This value is necessary to
exhibit tan "Dobie" markings]