Page 98 - JRT Magazine - 2023 Issue 2

Education

The dilution gene also can have lightening effects
on phaeomelanin, but it is less obvious and
can appear similar to a light tan or cream color. The possible genetic formulas for D locus
The nose color is the differentiating factor as are:
to whether the dog is a very light tan versus a
lemon. With a lemon (dd), the black nose (BB or • DD – homozygous for absence of the
Bb) is affected by the dilution and will appear liver dilution gene. This dog has normal
colored. eumelanin, and all its progeny will
have nondiluted eumelanin as well,
regardless of who it is bred with.
• Dd – heterozygous for the dilution
gene. This dog carries one copy for
absence and one copy for presence
of dilution. The dog itself will have
normal eumelanin, but it can pass
one copy of the dilution gene to its
progeny. In this case, the offspring’s
pigmentation will depend on the
partner’s genotype. Two normally
colored parents can produce a dilute-
pigmented pup if they are both Dd.
• dd – homozygous for presence of
dilution. This dog will have diluted
eumelanin and diluted coloration. This
dog will pass one copy of the dilution

Dilution-lemon. Note that the nose color has been diluted as allele to all progeny. Pigmentation
well as the red coat. and color of the offspring will depend
on the genotype of partner.
It is likely that the dilution mutation
occurred early in the domestication of
the dog, and it likely has occurred more
than once. It seems to exist in most, if not
all, breeds.

Locus E or Extension has the possibility
of two alleles in Jack Russell Terriers. The most
dominant one is Em. This allele will create a black
mask over the A locus pattern. The extent of the
mask can vary greatly. The most minimal version
is that the mask involves just the tip of the
muzzle, but it can also spread up to a fully black
face up to the ears, and in extreme versions, up
to the legs, chest, and undersides. Currently, the
Non-diluted light tan. Note that the nose color remains black. So,
this is not a lemon genetically, because it is not a homozygous modifiers responsible for the size of the mask are
dilute. unknown.

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