Page 97 - JRT Magazine - 2023 Issue 2

A similar issue can happen with heterozygous in the lightening of all eumelanin pigmentation
dominant black dogs (KbKy) that are black & tan in to paler shades. Black becomes grey/blue, red
locus A (atat). In this case, some red (tan) markings becomes lemon, and liver becomes isabella. The
on the face that are typical for tricolored dogs may dilution gene affects the intensity of eumelanin, not
be slightly visible, leaking through the dominant just in the coat, but also in the nose and eyes.
black, resulting in coloring called ‘ghost tan’. In JRTs
this modification is often not obvious because the The color of the nose provides a distinctive point
white spotting on the muzzle covers it. of reference. True diluted dd dogs will never have
a black nose; it will be blue. All eumelanin in a dog
Another variation that can occur with dominant with the dd genotype will be affected. True dilutes
black is called ‘bronzing’. This is not a genetic are often known as ‘born blues’. True dilute dogs
modification. It happens in various breeds (and not are born blue. If a dog is born with black hairs that
only in dogs) and is caused by sunlight and some turn grey with age and with the growth of coat,
dietary factors that destroy fragile black pigments it is not a dilute; rather, this effect is the result of
in the hairs, making them appear reddish. a separate greying gene. If a dog has any black
coloration at birth, it can’t be a true dilute.
With rough-coated, solid black dogs, both a blown
coat and clipping can affect the appearance of Since the JRT standards always demand a black
the color. The hair can appear silver. This also is nose, no JRTs with true dilution can be accepted as
not connected with genetics, but with grooming. meeting the breed standard.
When a hair shaft begins new growth from a
follicle, the color pigments are actively produced
only in the beginning. The base of the hairs lacks
good pigment. So, if a JRT coat is not properly
maintained with stripping to encourage constant
new coat growth, the coat will end up consisting
primarily of ‘old’ hairs that lack pigment and appear
grey. That grey is not the result of dilution and DNA
testing is not necessary for confirmation; some
correct hand stripping sessions will result in good
quality new hairs that will grow in fully black on
the ends. In contrast, dogs homozygous for the
dilute gene (discussed next) will have a silver/blue
color along the full length of the hair shaft and no
change can be made by hand stripping.

Locus D named for Dilute has just 2 possible
alleles: D – absence of dilution and dominant; d –
presence of dilution and recessive. This gene causes
a problem with the transport of pigments, resulting Dilution of a black tri is called a “Born Blue” Note the blue nose.

This progression is called greying and is not the result of the dilute allele, nor is it the result of creeping tan.

A Worldwide Magazine for the Jack Russell Terrier / Russell Terrier • Issue 2/2023 | 97