Page 91 - JRT Magazine - 2023 Issue 2

But the diversity of phenotypes expressed by the
A locus could not be fully explained by those four
alleles. Breeders of JRTs knew that to get a tri-
colored phenotype, a dog must be atat since the
black tan-point is recessive, but breeders could Ady – Agouti dominant clear
not determine whether the dog would ‘hold’ that yellow (i.e., referred to as
nice black and tan (tri) coloring for its lifetime or if tan in JRTs), with minimal or
it would fade from the perimeters inward. full absence of black-tipped
hairs.

Asy – Agouti shaded yellow,
Ay with a mix of clear yellow
(tan) and black-tipped hairs
and ranging from very light
shading to very dark. Black-
tipped hairs on shaded yellow
dogs can form a point on their
forehead called a “widow’s
peak”. It is a distinctive shape
that reminds some of a faded
A fading tri-color, also called creeping tan because the tan tricolor marking, but it is not.
creeps in from the perimeters of the dog toward the core as the
dog ages. Black on the tail and face at birth are soon changed to
tan. Black spots on the body are the last to change.

Abs – Agouti black-saddle
Fading: Same dog as a puppy and young adult.
(commonly referred to as
“faded tricolor”). The back
region and sides of the rib
cage are pigmented black
while the rest of the coat
remains clear yellow/red
at (tan).
Non-fading: Same dog as it ages. Note how the black is retained
strongly on the head as an adult.
Abb – Agouti black-back
(tan-pointed markings or
Fortunately, geneticists have continued their “black tricolor”). Dogs with
research, and by the end of 2020, new information this genotype will be fully
was published about the A locus which sheds black with tan markings
more light on these phenotypes. on cheeks, eyebrows, and
undersides.
For Russell Terriers, the two “old” alleles- Ay and
at- were each split in two for further classification,
and so today we have four possible alleles of agouti
series that can be found in our breed.

A Worldwide Magazine for the Jack Russell Terrier / Russell Terrier • Issue 2/2023 | 91