Extension, non-extension, & everything in between!

The E locus affects whether the basic color of the rabbit extends all the way down to the end of the hair or whether the basic color stops and another finishes. The extension gene controls expression of both black and yellow pigment, but different than agouti does. This gene is very unique in how the various genes function.

There are four genes on the E locus:

   Ed - dominant black (theoretical)
   Es - steel
   E - full extension
   ej - japense brindle/harlequin
   e - non-extension

Glittering Steel

Es

The (Es) is uniquely dominant over the wild-type gene of the E locus, and it is responsible for steel colored rabbits. However, steel is a tricky gene that is incompletely dominant. It is nevertheless overpowering as it over-produces black pigment on the hair, invading and taking over the normal pattern of color.

Gold-Tipped Steel (AA, Aat, Aa) + (EsE)	Black or Otter Steel* (atat, ata) + (EsE)	Black (aa) + (EsE)
*Depending on the intensity of the steel gene and modifiers, gold ticking may appear where the otter pattern is supposed to be.

A "correct steel" coloration requires a single steel gene and a single full extension gene, (EsE), as well as being agouti, (AA) or (Aa). The gene seems to be able to hide itself when combined with the other genes on the E locus.

Because of its nature, the (Es) gene occasionally seems to play tricks. As a dominant gene, (Es) supposedly cannot hide. A rabbit cannot be a steel if neither of its parents are steel. BUT, what if you have no idea that your "black" rabbit is actually an agouti black, other wise known as a double steel?

When homozygous, or doubled up on (EsEs), and depending on the strength of the modifiers you may get a rabbit that is virtually black - so dark as to overpower even the tipping of the hair. This often called agouti black, double steel or hidden steel, since it hides the presence of steel.

Likewise, when combined with japense/harlequin gene (ej) and non-extension gene (e), the rabbit may appear completly black with minimal to no ticking to give away the presence of the steel gene or they may also look like a normal (EsE) steel.

Additionally, in a self rabbit the ticking will not be present at all as it requires yellow pigment. It's black on black, with no ticking. Tan or otter pattern rabbits may also appear solid black as steel tends to turn the belly and undersides darker in a normal steel, however it may show the “ticking” where the tan/otter pattern is supposed to be aswell. Just depends on the intensity of the steel gene and its modifiers.

Full Extension

E

The (E) gene is the original dominant gene at the E locus and represent the "correct" or normal presention of black pigment. Like the other genes on the E locus, extension has a partial dominant so the recessive gene may show through. An example of this is a harlequinized agouti (Eej).

Chestnut (AA, Aat, Aa) + (EE, Eej*, Ee)	Otter (atat, ata) + (EE, Eej*, Ee)	Black (aa) + (EE, Eej, Ee)
*With (Eej) the harlequin/japnese pattern may be present on top of chestnut and otter. This depends on the intesity of the harlequin modifiers.

Japenese Brindle - Harlequin

ej

The (ej) gene is responsible for the harlequin or japnese brindle patter on a rabbit. This produces a striped or "block" effect of yellow and black pigment. When the rabbit doesn't have clear markings, this is called brindle.

In technical terms, the (ej) gene separates the black and yellow pigments putting them on different hair shafts. The gene only works properly when combined with chestnut (A), however, can show on otter and self rabbits.

Harlequin (AA, Aat, Aa) + (ejej, eje)	Fox Harlequin (atat, ata) + (ejej, eje)	Tort Harlequin (aa) + (ejej, eje)

It is believed that there are modifiers that affect how much brindling is on the rabbit. Some rabbits may appear to have light brindling or spotting (in the case of tri-colors) if the line has never encountered the gene before. While some have a lot of brindling or spotting.

If you combine harlequin with broken (Enen) or charlie (EnEn), the brindling or stripes become spots. This is what is known as a tri-colored.

Non-Extension

e

The (e) gene is the most recessive amongst the E locus. The gene is responsible for tortoiseshells (not to be confused with tortoiseshells in cats), reds, creams, etc. There is no extension of black pigment at all. Unless the effect is imperfect, possibly due to modifiers, you’ll get a remaining bit of “smut” or “soot” on the rabbit.

Orange (AA, Aat, Aa) + (ee)	Fox (atat, ata) + (ee)	Tortoise (aa) + (ee)

The Mysterious Dark Extension

Ed

There is a theorized fifth gene with the E locus that is even more dominant than steel. I have it listed below here as the jury is still out on whether it exists or not.

This gene is the (Ed) gene, also known as dominant black or dark extension. It supposedly takes the dark pigment extension beyond the normal agouti pattern, turning a chestnut or otter solid black. Some believe that this is really just a double steel (EsEs), as mentioned above.

If you know more about this gene, please let me know!