Rabbit Coat Color Gene E

The E/e gene controls whether the basic color on the rabbit (black, blue, chocolate, or lilac) is extended all of the way to the end of the hair shaft or whether the basic color stops and another finishes the hair shaft (such as the orange color on the back of a black tortoiseshell).  When a rabbit has full extension, it tends to look the same color all over, such as with a blue rabbit.  When there is non-extension, such as with a black tortoiseshell, the rabbit takes on a shaded look since the shorter hairs on the belly, guard hairs, feet and muzzle get only the basic color (they are not long enough to get the other color that finishes off the longer hairs).  That all sounds simple enough, but there is a complication.  Some C-series genes can also give a shaded look for a different reason (check out the sable gene, for example). 

I left out the steel gene, that is, the Es gene, on purpose.  It's a variant on the extension gene that has a surprising twist.  Usually the gene that is found in nature is the dominant variety.  But with the steel gene, it is actually dominant over the "E" full extension gene found in nature.  You need only look for steeling in full-extension animals:  black, blue, chocolate, lilac, etc.  It will never show up in "e-e" rabbits:  black tortoiseshell, chocolate tortoiseshell, blue tortoiseshell, etc.

Only one color of rabbit is called simply "Steel."   It has the genotype A- B- C- D- Es-.  It is genetically a steel-tipped chestnut.  All other colors are "steel-tipped," such as a "steel-tipped black."

A fourth e-gene exists, but is used only for creating tri-colored rabbits.  It is the Ej gene, which I will not deal with further since it is fairly rare in Holland Lops.

What's Going On Genetically

Since the Es steel gene is dominant over the other two "E-e" genes we'll discuss, there are three genotypes for the steel phenotype:  "Es-Es" (which may mysteriously cause the steeling not to show up), "Es-E" (steel carrying extension), and "Es-e" (steel carrying non-extension).  There are two genotypes for full extension phenotypes:  "E-E" (true-breeding full extension) and "E-e" (extension carrying non-extension).  As with all least recessive genes, there is but one genotype to have a non-extension phenotype:  "e-e."

What Happens When You Breed

Let's look at what happens when we breed a full extension rabbit that carries the non-extension gene with a steel-tipped rabbit carrying the non-extension gene (E-e x Es-e).  Since it only takes one Es gene to make a rabbit steel-tipped, 1/2 of the offspring, on the average, will be steel-tipped.  The other half is split between the full extension (carries non-extension) and the non-extension varieties.

The situation above is a very interesting one.  If we know that both parents are steel-tipped and we find that one or more of the offspring is non-extension (meaning each parent must have an "e" gene to donate to the offspring), then we can be certain that all of the full-extension offspring are steel, whether they show it or not.  Let's take the Es-Es offspring and see how the steel-tipping can suddenly seem to spring up from nowhere.  We'll breed it with a true-breeding full extension rabbit (E-E) and see the steel-tipping showing up in 100% of the offspring.

Breeding two of these Es-E offspring back together will produce 1/4 double steel genes that may not express themselves, 1/2 steel-tipped, and 1/4 full extension rabbits.  Since these are chances (25% chance) rather than definite outcomes, you could produce only the Es-Es rabbits in a litter (especially in a small litter) giving the appearance of a generation-skipping gene.  In fact, the Es gene could be hidden this way for two or more generations, giving the impression of "popping out of nowhere."  Let's look at the two Es-E rabbits' possible outcomes.

Of course, not all, and perhaps relatively few, Holland Lop breedings involve the steel gene.  Let's look at two full extension rabbits that carry the non-extension gene.  Notice that the two full extension rabbits can produce approximately 25% non-extension offspring.  This situation is what we have when, for example, we breed two black rabbits together and get a resulting black tortoiseshell kit.

Since there are so many combinations of "Es/E/e" genes when breeding rabbits, I won't attempt to make a complete table for each one.  But below you will see the possible combinations and the expected outcomes for each.  (Remember, these are averages--your exact results will vary, except when the percentage is 100, of course.)