Page 93 - JRT Magazine - 2023 Issue 2

The order of dominance for these four dominant yellow. Dogs with one of these
alleles is: genotypes at the agouti locus always
carry one copy of the dominant yellow
Ady Dominant (clear) Yellow > Asy Shaded gene and one copy of another allele from
Yellow > Abs Black-Saddle > Abb Black- the agouti series. The animal itself will
Back. always have clear yellow (tan)/red color
because allele Ady is the most dominant
With this, we have ten possible genotypes at in the agouti series, but the progeny
the A locus; four of them will be homozygous could have any colors from the Agouti
and six will be heterozygous. series, depending on the genotype of the

partner and which alleles are transmitted.
• 1) AdyAdy – homozygous for dominant
yellow. This dog carries two copies of this • 8) AsyAbs, 9) AsyAbb – two variants
allele, one of which will be transmitted of genotypes heterozygous for shaded
to its progeny. The animal itself and all yellow (commonly referred to as shaded
offspring will have clear yellow (tan)/red sable). The animal itself has shading
color, because this allele is most dominant (black tipped hairs) because Asy is the
in the Agouti series. second most dominant of the agouti
alleles and is dominant over Abs or Abb.
The color of the progeny will depend on
• 2) AsyAsy – homozygous for shaded genotype of partner and which alleles are
yellow. This dog may have black tipped
hairs, but this is not a tri colored JRT. It transmitted.
is simply a shaded sable. This dog will • 10) AbsAbb – heterozygous for black
always transmit one copy to its offspring; saddle and black-back. This dog will be
however, the color of the progeny will a black saddle “faded tricolor”, but it can
depend on the genotype of the partner have progeny of any color depending on
and what the other parent contributed the genotype of the other parent.
since this is not the most dominant allele.
• 3) AbsAbs – homozygous for black saddle
color. This dog will be a ‘faded’ tricolor. Previously, by use of the old version of tests
It will always transmit one Abs allele to for the A locus, we had just three possible
its offspring; however, the color of the formulas for Agouti locus:
progeny will depend on the genotype of
the partner. • AyAy – homozygous for dominant yellow
(tan/sable) dog, but it is unknown whether
• 4) AbbAbb – homozygous for black back the yellow would be shaded or clear.
with tan-pointed markings. As this allele
is the most recessive in the Agouti series, • Ayat – heterozygous dominant yellow dog
only homozygous dogs with two copies (tan/sable) that carried a ‘hidden’ tricolor
can be “black tricolor”. To have a chance pointed gene. It was unknown whether
in producing black back progeny (non- the yellow would be clear or shaded and
fading tricolors) from a black back dog we unknown whether the tricolor carrier allele
need to use a partner that carries at least would be ‘faded’ or not.
one copy of the Abb allele. • atat – homozygous tricolor dog. It is

• 5) AdyAsy, 6) AdyAbs, 7) AdyAbb – three unknown whether the dog would be a
variants of a genotype heterozygous for faded tricolor or black tricolor.

A Worldwide Magazine for the Jack Russell Terrier / Russell Terrier • Issue 2/2023 | 93