Genetics 101- Mini Rex are the breed of discussion, but this applies to ALL BREEDS!!! Just remember to change some of the names to suit your breed, such as changing the color name Castor to Chestnut (all breeds), Sandy (Flemish) or Copper(Satin coated animals).

The A Series

B is the second gene in genetic codes, and it stands for Black or Brown. Brown is to be associated with the Chocolate coloration, not brown rabbits such as Chestnut/Copper/Castor or Torts. ALL Rabbits are either Black or Chocolate, regardless of their outward coloration.
Most Chocolates will show a ruby glow to their pupil in subdued light, but SHOULD NOT be confused with the Shaded colors, who also show the same ruby glow to their eye. Shaded colors are from a different gene within the C series, and we will discuss that at a later time as well.

In order of Dominance, the B Series genes are :

B- Black (Blue IS Black, but diluted)

b - Chocolate (Lilac IS Chocolate, but diluted)

A rabbit has 2 genes on each series, and one is given from each parent. For a said color to be shown on a kit, one of its parents must have given it to the offspring. *The Dominant gene is the one that you "SEE"*, also know as the rabbits Phenotype. When both genes are known, that is call the Genotype. A rabbit with 2 identical genes is called Homozygous, and one with 2 different genes is call Heterozygous.

A rabbit will have its "Visual" gene and then can carry another identical one(Homozygous), or any one BELOW it on the series, but NEVER ONE ABOVE IT...that would mean that the rabbit is NOT the color you said it was in the first place (i.e.: A Chocolate carrying Black. The Black is dominant, so the rabbit would be BLACK Based).
Hence, a Rabbit that is Black colored can carry another Black gene, or a Chocolate gene.

A Chocolate Rabbit can *ONLY* be Homozygous for another Chocolate gene as there is nothing "Below it" to carry.

Some Examples of this in "color talk": 2 Black Based rabbits bred together can potentially produce Black Based, as well as Chocolate Based, providing that the Black based parents each carry a Chocolate gene.
2 Chocolate Based rabbits can ONLY produce Chocolate Based rabbits.

When speaking of the term Black, we mean that the rabbit's base color is Black. If it is an Agouti, the ear lacing will be Black. If it is an Otter or a Self, the ears will be Black. The color Tortoise, which has incorrectly been called a "Shaded" from time to time, is a SELF color, and will show those Black ears as well. The E series plays a role is where the "Shading-Like" color is distributed, and will be discussed at a later time. A REW, although can genetically be any COLOR under it's "white sheet" will also follow the same basic genetic principals. It IS a "SOLID COLORED" animal though, meaning that its body is the same color from nose to tail. The REW's coloration, or better yet, lack of coloration is from the albino gene on the C Series which prevents pigment from developing on the actual hair shaft and eye. The C Series will also be discussed in great detail in a later article. A REW rabbit can genetically be a Black Or a Chocolate, and once you understand genetics, you will be able to test breed, or read a pedigree and come to a proven conclusion on your own!

What is nice about knowing genetics and your rabbit's Genotype and Phenotype is when purchasing animals that come from GENETICALLY IMPOSSIBLE backgrounds. Someone obviously made a mistake on the happens to all of us. There are also colors that "mimic" others, and unless you know the Genotype, these colors in mime can really throw a wrench into your breeding program. Also another thing to remember, is that because a color is not recognized in your breed's STANDARD, does NOT mean that is cannot exists in your BREED! Recessive genes can be hidden for many many generations, and can only produce themselves when they meet up with another like or more recessive gene.

An example of the ONLY genetically impossible breeding in the B Series:

Chocolate X Chocolate - Black (Chocolate does not have a Black gene to give)

I am making a notation of this genetic impossibility because many people who are just starting in rabbits are purchasing more stock than breeding them. If you want to breed for certain colors (or avoid them), then you need to be able to tell what is in your gene pool. I breed mainly CHinchilla Mini Rex, so I DO NOT want to add a Chocolate gene into my gene pool, as this will produce Chocolate Chinchilla later down the road, an unshowable color, and almost impossible to eradicate!

The percentages of a given color that are shown on many websites and genetics books are not a percent per litter, it is the chances that EACH KIT has of being a certain color or pattern. Such as, a Black to Black cross and they both have a Blue parent, each KIT has a 50% chance of being a Blue, not 50% of the litter. With that genetic average, the same cross could potentially produce 100% Blues. Murphy's Law tends to prevail, and if you are trying to produce that particular color, it will stay recessive almost indefinitely...LOL!

By looking at the pedigree, you may be able to Genotype your animals.
If an REW rabbit, that has only produced Chocolate kits when bred to another Chocolate, has one parent being an Chocolate, and one parent being a Black on the pedigree, this becomes easier.
*We know from reading above that the Chocolate can only ever carry itself, so the Chocolate parent is "bb".
* We know that the Black parent is dominant for "B", and since it produced an ONLY Chocolate producing baby, it is MOST LIKELY recessive for "b".
Just by that basic information, we know that the REW rabbit in question is probably "bb", one gene from each parent. The Black parent is "Bb", and the Chocolate parent is "bb", as all Chocolates are.

A punnet square below illustrates this cross, and you can substitute other crosses accordingly.

In percentages, each kit has a 50% chance of being an Black animal that is recessive for Chocolate and 50% of being a Chocolate