Page 99 - JRT Magazine - 2023 Issue 2

There are three possible formulas for Locus E in
JRTs:

• EmEm – homozygous for the mask extension
allele. This dog will have a facial mask and all
its offspring will have one as well. The amount
of white spotting and the base color of the dog
will affect how easy it is to see the mask.
• EmE – heterozygous for the mask extension
allele. This dog has one copy of the Em allele
and one copy of normal extension (no mask)
allele. The dog will have a black facial mask
itself (visibility depends on base coloring of the
dog and whether white spotting is extensive).
The progeny of this dog may or may not have
a mask, depending on the genotype of the
partner.

• EE – homozygous for normal extension. The
E allele indicates an absence of mask or any
other effect. This dog will have no mask. Its
offspring can be with or without a mask,
depending on genotype of the partner.
There is one other known allele for the E locus, but
its presence has not yet been proven in JRTs. The
allele e is for recessive red. This allele is the most
recessive inside the E locus, but it is dominant
over almost all other loci. Expression of this allele
is possible only when the dog is homozygous (ee).
All have black masks (Em), hidden to different degrees by the
effects of the Sp allele. Dogs with the heaviest black masks Dogs with ee will be red in that the skin cells of the
presumably are homozygous EmEm, but homozygous SpSp can dog are unable to produce eumelanin in the coat,
hide much of it.
but the nose, eye rims, and lips remain black. The
intensity of the red can vary greatly. Recessive
In JRTs, the white markings on the muzzle can fully red ee color looks very similar to unmasked clear
hide minimal versions of a mask. In addition, the yellow (Ady) but can be differentiated by the color
mask can exist, but will be invisible, on dominant of the whiskers which turn red or light-colored for
black dogs and may be very difficult to detect on recessive red ee dogs. Again, it is not clear that ee
black-back, tan-pointed dogs (non-fading tri). exists in JRTs.

Masks (Em) can be hidden quite significantly by the piebald white spotting (Sp) in JRTs.

A Worldwide Magazine for the Jack Russell Terrier / Russell Terrier • Issue 2/2023 | 99