The fifth segment of Silver Fox Genetics 101 covers the E-locus and that would not be “E” for easy but for extension. This is another one of the loci that we take for granted in the Silver Fox breed, although there are four possible alleles for the E-locus that can only hold two, one from each parent. “Es” steel is one of the “E” alleles that was already covered in the last segment on the A-locus, because of the way that it works with “A_” agouti.
Ideally, the Silver Fox should have homozygous “EE” on the E-locus for full extension, that is to say that the color fully extends on the hair shaft. If you are thinking back to the A-locus of the “aa” self hair shaft already being fully colored, you are probably wondering if this is the same thing. Actually, this is why we need to understand the interaction between the A- and E-loci, because they work differently and yet act upon each other to confuse us about the actual underlying genotype. As stated in the previous segment, the hair shaft is fully covered on all the coat of the “aa” self rabbit, so that even with “Es” steel the appearance is still a solid rabbit. This is why Silver Foxes can be “aa Es_” and look exactly like it is “aa E_,” so although we would like to assume that “E_” is on the E-locus on a standard colored Silver Fox, we probably should not.
I need to address one thing before moving on. The order of dominance is finite, but opinions vary about them. I have read many sources that place “E” as the highest in dominance and some that place “Es” as the highest. Both have capital letters, both are dominant, but I believe steel is the more dominant. Just because it does not show on an “aa” self or a “cc” red-eyed white or an “A_ EsEs” agouti super steel or possibly an “A_ Ese” agouti steel with non-extension, does not make it less dominant over “E” in the E-locus. When “Es” steel and “E” full extension are both present, it is written “EsE” not “EEs," which more than suggests that geneticists considered steel to be the more dominant of the two.
These are the possible alleles on the E-locus in order of dominance:
- Es - steel
- E - full-extension
- ej - Japanese or harlequin (brindle)
- e - non-extension
The one allele should we never see in a Silver Fox is “ej” which contributes to brindling, harlequin, and tri-color patterns in other breeds. However, the “Es,” “E,” and “e” are often found in the Silver Fox, although “e” is less common.
Homozygous “EE” would be the most desirable allele combination on the E-locus for Silver Foxes. However, "EsEs," "EsE," "Ese," and "Ee" will all look exactly the same as a homozygous “EE” rabbit because of the “aa” self-color that has dominance in covering the entire hair shaft. Many will write in the genotype as “E_,” but that may be an erroneous assumption because “Es” may be the dominant allele and, as discussed previously, steel is often found to be “carried” (although not a recessive) in Silver Foxes, because it is not seen on an “aa” self rabbit. In effect, “Es” acts like “E” on an “aa” self rabbit.
To “E_” or to “Es_”? That is the question. Typically, you will not see “Es_,” steel with an unknown second allele, written on any genotype for a Silver Fox. Steel is mostly ignored until seen in offspring from a cross-breeding with an “A_” agouti or “at_” otter. However, when you see “E_,” extension with an unknown second allele, written as the genotype, you should understand that it may not be accurate even though it seems to agree with the phenotype (how it appears).
- aa EsEs – solid (self homozygous steel)
- aa EsE – solid (self steel with extension)
- aa Ese – solid (self steel with non-extension)
- aa EE – solid (self homozygous extension)
- aa Ee – solid (self-extension with non-extension)
- aa ee – tort (self homozygous non-extension)
It looks very confusing, but if you examine this list you will see that regardless of whether it is “Es” or “E” as long as there is one dominant in the E-locus, the Silver Fox will be a solid color as it should be.
Did you notice the one that is not like the others? Assuming there is no “ej” on the E-locus (as there should not be), the only funky color that you might see from the E-locus is when two rabbits carrying recessive “_e” non-extension are bred together. The homozygous recessive “ee” rabbit is called a tortoiseshell or "tort" for short, which is orange blending into black, blue, chocolate, or lilac, depending on the alleles present on B- and D-loci, at points like the nose, ears, feet and along the sides to the underside. However, due to other modifiers we would not see (or may not even have in the Silver Fox) called rufus (meaning red), torts can vary in richness of tone to deeper reds also.
Tort is not a desired color in Silver Foxes unless you are working toward the Alaskan Red Fox, another rabbit breed that was being developed by the same Walter B. Garland, the developer of the original Silver Fox, before he passed. As I understand it, the original Red Fox's Certificate of Development submitted to the American Rabbit Breeders Association (ARBA) stated that it may be silvered. Ideally, it was a black tort with the stand-up “Fox” fur and the richer red coloring from high rufus modifiers, but slightly smaller than the Silver Fox. Because of changes in standards for a new breed, breeders on this project at present seem to be leaning towards the tort as a variety of the Silver Fox breed rather than a new breed.