Basic Genetics Facts

Why Rabbit Coat Colors?

choc-lilac

These rabbits differ in only a single allele. The rabbit on the left is a Lilac Otter (genotype: at- bb C- dd) and the one next to it (her dad) is a Chocolate Otter (genotype: at- bb C- Dd). Normally I would not be able to fill in the second allele on the D-locus, but because he produced a lilac daughter I know that it MUST be ‘d’.

  • Complex enough to be interesting
  • Can include or exclude various genes or alleles without loss of realism
  • Includes visual effects of
    • Simple dominance
    • Simple recessives
    • Co-dominance
    • Incomplete dominance
  • Rabbits are classified by color according to phenotype but bred according to genotype.

Rabbit Coat Colors determined by 4 basic gene series*:

  • A: “Agouti” pattern (how colour appears on hair) [3 alleles: A, at, a]
  • B: Black vs Brown [2 alleles: B, b]
  • C: Colour [4 alleles*: C, cchd, ch, c]
  • D: Dense vs Dilution [2 alleles: D, d]

Basic wild color (Agouti) looks like:

  • A- B- C- D-

*There are in fact a few more (not counting modifiers) but these are the most obvious ones, visually speaking

Basic Genetics

All genes come in pairs. If both genes of a pair are the same, it is said to be homozygous for that trait.

Genotype refers to the gene itself, while phenotype refers to what we can see. Sometimes a phenotype will imply a certain combination of genes but the actual genotype is different. The best way to discover an animal’s genotype is through test breeding with an animal whose genotype is known.

 

Gene Labels

Genes are usually coded (written out) as single letters with possible superscripts (cchd). All alleles in the same locus will have the same main letter, and the dominant genes are written as upper case letters (C) while the recessive alleles are written in lower case (c).

For more on gene nomenclature try here (wikipedia)

The rules for rabbits and other furred animals are similar to those for rats and mice.

There are 8-10 main groups of colour genes in rabbits, each controlling a different aspect of the colour and markings. This game will use the first 4.

The genes within each group are listed in decreasing order of dominance. A Capital letter denotes a dominant gene.

 

PATTERNS [A / at / a ]

A = agouti
at = tan (otter)
a = self

The pattern gene controls how the colour appears on the hair. The dominance relationship for these genes is quite simple: each allele is completely dominant over the ones ‘below it (as listed above). This means that the following pairs will all look exactly the same: AA, Aat, Aa. They will all look like agoutis. A tan (or otter) can be atat or ata, and a self can only be aa. Unless you know the genetic make-up of the parents, it is not possible to tell what the second gene is on an agouti or tan without test breeding.

Castor - Black Agouti (A- B- C- D-)

Castor – Black Agouti (A- B- C- D-)

Agouti Fur - Castor (A- B- C- D-)

Agouti Fur – Castor (A- B- C- D-)

Agouti is the basic “wild” colour. Hairs on different parts of the body are coloured differently, but will have three-five different coloured bands on each hair. This pattern looks different on a rex because of the shorter hairs. The bands are smaller and the colours appear more intense. The Castor is the name given to the black agouti (the standard wild colour). Their hairs should have at least three rings: the undercolour should be slate grey; the intermediate colour should be as rich an orange or rufous red as possible, and the tips should be black.

 

Black Otter (at- B- C- D-)

Black Otter (at- B- C- D-)

Tan Markings - Black Otter (at- B- C- D-)

Tan Markings – Black Otter (at- B- C- D-)

The otter (called tan in most other breeds) should have a solid body top colour with a lighter undercolour (next to the skin). The underside (from chin through belly to tail) should be white on the surface with a grey undercolour, and there should be a redish line between the body colour and the undercolour. The insides of the ears, and around the nose and eyes should also be reddish (i.e. red or orange in full coloured [black or chocolate] rabbits and tan or cream in dilute [blue or lilac] rabbits).

Black - Self - (aa B- C- D-)

Black – Self – (aa B- C- D-)

The self rabbits should be exactly the same colour all over their bodies right down to the skin.

The three rabbits shown here all have the same genes EXCEPT on the A – all are black (B- D-) with full Color (C-).

 

COLOUR

There are only two alleles in this group: the “black” results in more intense looking colours and the brown changes the black parts of the rabbit to brown. This means that in the Castor for example, the tips of the hairs become brown instead of black, making the rabbit look much redder.

B = Black
b = Chocolate

 

Chocolate Otter (at- bb C- D-) VS Black Otter (at- B- C- D-)

Chocolate Otter (at- bb C- D-) VS Black Otter (at- B- C- D-)

COLOR / SHADING

The shading (or colour) gene controls the amount of pigment in the hair; relative amounts shown as units of black ‘B’ and yellow (or red) ‘Y’ colour. Imagine that the total amount of pigment in hair is the same for all hairs. As a result, shorter hairs appear darker (and also why long-haired varieties look faded). This explains the shading pattern found in seals, sables, torts, and the pointed colours. The colour pattern of the chinchilla (cchd) is essentially the same as that for the agouti except that is lacks the reddish colour in the mid-band.

C = Normal [BBBBYYY]
cchd = Dark Chinchilla [BBBBY–]
cchl = Light Chinchilla [shaded : seal & sable] [BB—–] *Note: We are not using this gene in our game.
ch = Himalayan [BB—–]
c = White [Albino : absence of colour] [——-]

 

castor-2010-04-23_12-49-10

Castor - Black Agouti (A- B- C- D-)
Castor – Black Agouti (A- B- C- D-)

This rabbit is the same PATTERN as the one below.


Chinchilla (A- B- cchd- D-)2013-03-30_14-01-10_wm

Chinchilla (A- B- cchd- D-)

Dark chinchilla removes most of the yellow band. It makes the skin look brown but takes the red color out of the hairs. Note that a chocolate chin retains the brown hue in the tipping but has completely lost it from the midband.


Californian - Black Californian (A- B- ch- D-)  This one is still young and his full colors have not yet developed).The Himalayan gene is affected by temperature – it prevents color from forming if it is too warm. That’s why the color only appears on the extremities.
Californian – Black Californian (A- B- ch- D-)
This one is still young and his full colors have not yet developed).

 

 

 

 


Red-Eyed White (-- -- cc --)Albinism is epistatic – it actually masks the expression of other genes. The albino gene prevents pigment from forming and so the entire animal lacks color (including the eyes). The other color genes are still there – you just can’t see them.

 

 
Red-Eyed White (– — cc –)

 

DILUTION

Controls the “intensity” of the colour: a diluted black is a blue, and a diluted brown is a lilac. The dilution affects the whole rabbit, not just the hair colour. This includes the pigmentation in the skin and the eye colour.

D = Full Strength (Dense)
d = Diluted

Black (aa B- C- D-) VS Blue (aa B- C- dd)

Black (aa B- C- D-) VS Blue (aa B- C- dd)

We can look at the colour (black vs brown) and the dilution genes together:
– B- – D- – = Black (where the – represent A, C, and E)
– B- – dd – = Blue
– bb – D- – = Chocolate
– bb – dd – = Lilac

Together, these two genes account for the four main colour variations of all the other shades and patterns. For example in the agouti group we have: castor (black), opal (blue), amber (chocolate), lynx (lilac).

 

Black - Self - (aa B- C- D-)

Black – Self – (aa B- C- D-)

 

Blue (aa B- C- dd)

Blue (aa B- C- dd)

 

Chocolate (aa bb C- D-)

Chocolate (aa bb C- D-)

 

Lilac (aa bb C- dd)

Lilac (aa bb C- dd)