Dominant Bunny

Behaviorally, Leo was our dominant bunny and Katy the submissive (I always called her "phlegmatic") partner.

Genetically, who had the dominant genes?  Let's investigate their fur coloration genes.

What follows is a basic explanation of the genes that affect fur coloration.  I started reading about this tonight because of comments that have arisen in response to my daily rabbit postings on FB, and it's really interesting stuff.  But I would understand if you want to skim over this part.

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There are five series (loci) of genes, labeled A-E for reasons that will be clear below.

A=Agouti pattern.  This refers to the presence or absence of banding on the hair shaft, which affects the pattern of coloration, not the color of the hair itself. 
Dominant: A - agouti - the hair shaft has bands of color that give the bun the light-to-dark pattern over the fur.  The bands are (moving from skin-end of hair to tip) white, gray, rufous (reddish orange), and black.  This is the familiar "wild rabbit" look.
Intermediate: At - otter, aka tan -  same as agouti only the main part of the body has hair shafts with a solid color.
Recessive: a - self - the hair shaft is a solid color so the rabbit has a solid coloration pattern over the entire body (and the fur is a solid color down to the skin).

Katy:  Definitely had an agouti coloration. (Could be AA or Aa.)
Leo:  ???

B=Black coloration.  Affects the intensity of the black pigment.
Dominant: B - black
Recessive: b - brown (aka chocolate)

Katy:  Definitely had a black coloration.  (Could be BB or Bb.)
Leo:  I think he also had a black coloration.  (Could be BB or Bb.)  The fact that he was bred to Katy further suggests this because typically people breed the same color together.

**Note that when you combine the dominant A (agouti) and B (black) genes, you get a rabbit like Katy who looks brownish, not black, because of the banding of the hair shaft given by the agouti gene.  (Remember that one of the bands is a reddish color and that shows up in her pattern of coloration.)  Only a self black, with no banding to the hair shaft, will look black.

C=Complete color. This affects the shading or albinism of the rabbit.  There are five options here, listed in order of most to least dominant.
Dominant: C - complete - all pigments normal
cch3/cchd - chincilla - black is normal, yellow pigment becomes white
cch2/cchl - shaded - reduces the black pigment, eliminates yellow pigment
cch1/ch - himalayan or californian - color is restricted to the "points" (like on a siamese cat), the rest of the body is white, and eyes are red.  What's weird/cool is that this is temperature sensitive!  The color only shows up on the cool areas (the extremities).
Recessive: c - albino - no color and red eyes, aka red-eyed white (REW)

Katy and Leo:  Definitely had a complete coloration.  (Could be CC or C with another type.)

D=Dense color.  Affects how much black or brown pigment (from the B locus) is present.  Does not affect the intensity/chemical composition of the pigment itself.
Dominant: D - dense
Recessive: d - dilute - gives a faded look (black becomes blue, chocolate becomes lilac)

Katy and Leo:  Definitely had a dense coloration.  (Could be DD or Dd.)

E=Extension of color.  Affects the quantity of black pigmentation.  There are four options here.
Dominant: Ed - dominant black - will make any rabbit look black.
Es - steel - overproduction of black on the shaft makes the bun look darker.
E - normal extension ej - Japanese - the yellow and black pigments are in separate areas instead of on the same hair shaft, creates the brindled mix of colors of the harlequin/magpie.
Recessive: e - no black pigment at all, turns the rabbit red/fawn.

Katy and Leo:  Definitely had a normal extension.  (Could be EE or E with another type.)

So no wonder we see Katy-looking rabbits so often -- the castor rex is what you get when your bun has at least one copy of the dominant gene on each of the 5 loci!

But there are other genes that also affect the coloration pattern.  Here is one that's important for my buns:

En=Broken factor (English spotting gene).  Gives the rabbit that Leo look of the color "broken up" with white areas.  Present in some breeds (such as mini rex).
Dominant: En - broken
Recessive: en - non-broken

A rabbit with two En genes (EnEn) is called a Charlie and has very little non-white color.
A rabbit with one En and one en (Enen) is a normal broken.
A rabbit with two en genes (enen) is non-broken.

Katy:  Definitely had non-broken pattern.  Must be enen.  Recessive on both.
Leo:  Definitely had a normal broken pattern.  Must be Enen.  Dominant on one, recessive on the other.

There are also plus/minus modifier genes that affect how much of the white and dark colors will appear on the broken colored bunny--whether it has the "blanket" of dark color or the "spots" of dark color (like Leo).

Others include Du (dutch factor--gives that sharp white triangle and other markings of the dutch rabbit), Si (silvering--creates silver hairs), V (vienna--creates a blue-eyed white rabbit), W (wideband--the yellow band of the hair shaft is larger), and P (changes eyes to pink).  These are recessive, i.e., require two of the recessive genes to show up on the bunny, and neither of my buns had these them.

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OK it looks like Katy was dominant on all genes (i.e., at least one of her pair for each loci must be the dominant version of the gene) except the broken coloration (10 out of 11).

Leo...harder to say.  He was dominant on somewhere between 9 and 11 out of the 11 genes, but if I had to guess, I would say 11 of the 11.

It would not be implausible to me that Leo was an exceptionally dominant rabbit even where his coloration genes were concerned.


My thanks to the following web sites, from which I gathered the genetic information above and hopefully did not mangle it too badly in the process:

http://www.raising-rabbits.com/rabbit-coat-color-genetics.html
http://www.sleepyhollowrabbitry.com/genetics.html
http://www.3chobbyfarm.com/Rabbit-Genetics.html
http://mosaicrabbitry.weebly.com/rabbit-coat-color-genetics.html
http://rexrabbit.tripod.com/brokengene.html
http://www.threelittleladiesrabbitry.com/blog2/2011/04/06/the-en-or-english-spotting-gene-in-rabbits/