There are a few terms that vary between breeds (in Angoras, a
fawn is the regular shade of 'yellow'
ee, and the dilute shade is
cream; in other breeds,
fawn is the dilute, and
orange is the full color variety.) What to call a chinchilla with fawn
ee, varies as well, almost none sanction it for showing, but it is called ghost chinchilla, fawn chinchilla, ermine, or frostie/frosty. Agouti with blue is sometimes called
opal, agouti with lilac can be
lynx, and agouti with chocolate can be
cinnamon. Other than those naming quibbles, the genetics between the breeds is pretty much the same. For the Rex, we add the
rex recessive, and for satins the
sa satin recessive.
The short version of rabbit genetics: there are five main genes to be concerned with in rabbits, conveniently coded
A, B, C, D and
E.
1. A is for agouti--this is the wild rabbit color, with multiple colors on one hairshaft, which we call 'rings'. You might see multiple sets of rings when you blow into the coat, but the basic set is an undercolor, the middle yellowish 'fawn' band, the outer band (the main color), and a tip. Agouti rabbits also have special markings, such as a white belly, white rings around the eyes and nose and under the chin, white inside the ears. Agouti is dominant, you only need one agouti
allele (a single version of a given gene) to be an agouti. We use capital letters to denote the dominant version, and lower case letter for the recessives. So, if a rabbit gets a dominant agouti gene from one parent,
A, the other parent can donate either another dominant version
A, or the recessive non-agouti
a, and still look the same. We call the rabbit with two alleles that are the same
homozygous, homo- means 'the same'. When a bunny gets two different alleles, we call them
heterozygous, hetero- means 'different'.
The recessive version
aa, is all one color. While the fiber may get paler towards the skin, it is all variations of the same color, with a colored belly, colored ears, no white markings. We call these non-agouti rabbits a
self pattern. When you look into a nestbox of newborn bunnies, you might not notice any difference between an agouti, and a solid non-agouti color, except for the white inside the ears on the agoutis. That shows up really quick, before any of the other markings. Both of the kits here look black, but the one on top left has black inside the ears, a self non-agouti black; while the one on the bottom right is an agouti, you can see the white inside the ears.
Here's the same two rabbits (with a chocolate agouti in the middle) a few weeks later:
No question that the black agouti on the left (called a chestnut agouti), looks different from the self non-agouti black on the right. The self rabbit has a black belly, no white markings. The chestnut agouti has the white around nose and on the belly (can't see the white ringing the eye or in the ears in this photos), as well as the bands of color coming in. The chestnut colored outer band with black tip is now quite visible.
There is an intermediate version, dominant over non-agouti but recessive to full agouti, called
tan, sybolized by a lower case 'a' with a superscript 't' (for tan). Since I don't see a good way to do that here, I'll use
a(t). Tan has the agouti markings, but no rings on the hairshaft. However, a bit of color on the tips of the hair may remain, called
ticking. True tans also have a reddish modifier called
rufus, that fills in the white agouti markings with an orange shade. Usually in most breeds, we have tan variations called
otters and martens. Mixed with the full-color 'C' gene, you get
otters, where the white markings get a line of tan around the edges, maybe a little tinting of the markings as well. Mixed with the chinchilla gene, that we'll talk about later, you get
martens, with all-white markings, no tint.
2.
B is for black/brown This is an easy one. All rabbit colors are based on the pigment
melanin. It's what shades our skin in the sun with a tan, and gives our hair and skin color. There are two main versions of melanin,
eumelanin is the dark version, for browns and blacks. That is the version that the 'B' gene controls. The dominant full eumelanin version is called black, and you only need one copy of to be black, either
BB or
Bb is black. The recessive less-eumelanin version is called brown, you need two recessive
bb copies to be brown. Let's skip over 'C' for the minute, and finish the main color possibilities. . .
3. D is for dense/dilute This gene either crowds the pigment together (dominant 'dense'
D, or spaces the pigmented cells out more giving less color, the recessive dilute
'd'. Again, you only need one dominant 'D' to have full dense color, it takes two recessive dilute
dd to be a dilute. The dilute of black is called 'blue', a lighter gray color. The dilute of chocolate is called 'lilac', sometimes described as 'pinkish dove gray'. That gives you the four main dark color varieties, black, chocolate, blue and lilac. The non-agouti self colors come in those four varieties, as do agouti and tan patterns.
4. E is for extension, which simply means that the normal color pattern is extended normally to the tip of the hairshaft. There's one more melanin possibility, which is a recessive on this gene,
ee, called 'fawn' or 'non-extension'. Sometimes, enzymes will turn off the dark eumelanin, and instead produce a yellow-based color with
pheomelanin. That's what gives us our fawn/orange colors, and is the middle band on most agouti patterns. There's another recessive modifier called
wide-band (ww) that can take that middle yellow band and extend it clear out to the tips of the fiber, making a golden/orange looking rabbit. It will still have the agouti markings, but not the banding, usually having a plain white undercolor with the orange.
If you combine recessive
ee with non-agouti
aa, you get a strange combination called 'tortoiseshell'. This self fawn has the yellow/orange body hair, but produces the normal dark color on the face, ears, legs and tail, and shading up a bit onto the body.