Page 95 - JRT Magazine - 2023 Issue 2

Liver-nosed JRTs. Genotype at locus B is homozygous bb. The bb causes any eumelanin pigment to lighten to liver or chocolate. This
includes eumelanin in the eyes, thus, the gold or green cast, similar to that which may result with dilution at locus D, but bb alone can
cause this even without dilution. The dog on the upper left is sometimes called a brown tri by breeders. The liver nose is not acceptable
in the breed standards for JRTs, Russells, or Parsons in any country; however, there are no health consequences.

Locus K or Dominant Black was a very
popular subject in recent years among JRT
lovers. Bicolored black & white dogs have
always existed in the original English bloodlines
and from there, they were imported to USA,
France, Finland, and a few other countries. For
unknown reasons, the bicolor black & whites,
together with tricolors, were considered less
attractive and pushed out little by little by
the tan & white JRTs. In contrast, bicolor and
tricolor Fox Terriers were most popular. In any
case, bicolor JRTs were not imported in enough
quantity (if ever) from the UK to Australia where
later were made almost all dominant ‘show’
lines in our breed. So, in a relatively short time,
the color almost disappeared from the genetic
pool. Today, however, black & white dogs have
gained interest and so an understanding of their
genetics is important.
Kbr- Brindle does not exist in purebred JRTs. Somewhere in the
past ancestry of the dog pictured, a Dachshund, Cairn, Corgi,
or other breed that naturally carries Kbr was purposefully or
accidentally introduced.

At locus K, there is a possibility of three alleles,
one of which is Kbr makes brindle, which is
unacceptable and does not exist in purebred
JRTs/Russell Terriers. Two other alleles, Kb and
ky, may be found in our breed and both regulate
the expression of black eumelanin. Dominant
black Kb allele will make a dog solid black by
blocking and ‘covering’ any expression of red
pigment phaeomelanin. Allele ky is recessive,
and it acts in an opposite manner by letting
phaeomelanin appear in the coat. The dominant
K locus black is found in dogs only. In most other
Bicolor black/white is the result of the dominant K.
mammals, black is recessive.

A Worldwide Magazine for the Jack Russell Terrier / Russell Terrier • Issue 2/2023 | 95