Page 94 - JRT Magazine - 2023 Issue 2

Education
It is now possible to DNA test for the extended
agouti series at the UC Davis (USA) laboratory and
Vetgenomics laboratory (Russia). These new tests
will provide precision in knowing whether a future
tri-colored litter might ‘fade’ or not with age.
Black saddle tri color, showing the tan creeping into the black
over time. Also called a faded tri.
Prior to the discovery of these new alleles at locus
A, it was believed that the modifier RALY gene
located on the chromosome in the same area as
the “old” allele at was determining the ‘fading’ of
tricolors. But results of DNA testing often were
contradictive to the phenotype and today we
know why that was. It is possible that RALY may
have some influence on the process and hopefully
researchers will soon elucidate these interactions.
Normal greying/ageing of a shaded/tipped sable.
94 | A Worldwide Magazine for the Jack Russell Terrier / Russell Terrier • Issue 2/2023
Locus B is named for Brown as the
genes located here determine which basic
eumelanin pigment a dog will have – black
or brown (liver). It is important because
liver pigment is unacceptable in our breed.
Every breed standard for the JRT/ Russell/
or Parson, no matter which kennel club,
state that the nose must be black.
This locus includes just two possible
alleles: B – by which will be produced black
eumelanin and b that will transform all
black pigments to liver/brown. Expression
of allele B is dominant towards allele b, and
so the possible genetic formulas for this
locus and their expression are:
• BB – homozygous for producing black
eumelanin. The dog carries two copies
of the gene for black eumelanin, and so
the dog itself and all its progeny will
have black pigment.
• Bb – heterozygous for producing black
eumelanin. This dog carries one copy
for black pigmentation and one copy
for liver pigmentation. The dog has
black pigment itself, but it potentially
can produce progeny with liver
pigmentation if bred to another dog
carrying b.
• bb – homozygous for producing liver
eumelanin. This dog carries two copies
of the allele for liver pigmentation. This
JRT has unacceptable liver pigmentation
itself, and it can produce progeny with
liver pigmentation as well, depending
on the genotype of its partner.
Although rare in JRTs/Russell Terriers, the
b allele for liver exists in our breed. Puppies
with liver pigmentation still occasionally
occur in purebred Jack Russell Terriers,
including in popular lines, and so there
are carriers in the gene pool. DNA testing
for the B locus is recommended, not to
remove carriers from breeding programs
but to ensure carriers are bred to clears to
maintain a black nose.