If you are going to have breeds like Havanas where there are only a few varieties recognized it can be relatively easy to determine their genetics. When it comes to color genetics there are really only two colors, BLACK and YELLOW, there are then genes that modify these two colors possibly making hundreds of different rabbit colors.
Let's start with the easy stuff. If you are curious about genetics it will most likely be to your benefit to start with the basic varieties. I consider the basic varieties to be black, blue, chocolate, and lilac. Doing this you can learn how things are affected. In order to understand these 4 varieties we have to know that a rabbit receives 2 of each coat color gene one from each parent.
The B Locus
Starting with the B locus. The B locus is what can give you Blacks and Chocolates, where black is dominant to chocolate. A chocolate gene is represented as an uppercase (B) and a chocolate gene is represented by a lowercase (b). So in the B locus you can have 3 different variations in genotype.
BB - This rabbit would appear black and it carries black so it can only pass on a black gene to its offspring.
Bb - This rabbit would also appear black, but it carries the chocolate gene, and can pass on a black gene or a chocolate gene to its offspring. If you breed two blacks and get a chocolate, they are both genetically Bb.
bb - This rabbit would appear chocolate, and would pass on only chocolate genes to its offspring.
The D Locus
Yes I know I skipped C but for the basic varieties you only need to worry about the B and D locus. The D locus is what gives you dilutes, your blues and lilacs. Blue is the dilute of black, and lilac is the dilute of chocolate, and blue being the dilute of black is dominant to lilac making lilac the most recessive of the four. A dense (dense means chocolate or black) gene is represented by an uppercase (D) and a dilute gene is represented by a lowercase (d). So just like the B locus you can have 3 different variations of genotypes .
DD - This rabbit would appear chocolate or black depending on the B gene . It also carries the dense gene so it can only pass on a dense gene.
Dd - This rabbit would also appear chocolate or black, but it carries a dilute gene and it can pass it on to its offspring. So if you have two dense rabbits and they have a dilute offspring, the parents would be genetically Dd.
dd - Now this rabbit will appear to be blue or lilac, again dependent on the B gene. This rabbit will then pass on the dilute gene to its offspring.
Still with me? well let's put it together and maybe it will be a bit easier
Putting It Together
Because everything relies on each other this can be confusing, but by looking at a pedigree and test breeding, after a little bit the basics will become easy and you can start learning more complex colors!
BBDD - Black (carrying black)
BBDd - Black (carrying dilute)
BBdd - Blue
BbDD - Black (carrying chocolate)
BbDd - Black (carrying chocolate & dilute)
Bbdd - Blue (carrying chocolate)
bbDD - Chocolate
bbDd - Chocolate (carrying dilute)
bbdd - Lilac
Remember a chocolate will always pass on a chocolate gene and a dilute will always pass on a dilute gene. The best way to introduce new colors is by knowing the genotype of your rabbits and knowing what more you will need.