Mary Allen
With only two pigments, nature conjures up all the colorful rabbit breeds that we can admire at exhibitions. Understanding the rules behind color inheritance helps in breeding your desired color and is exciting.
The starting point of all rabbit colors is the wild color, the grey-brown camouflage color of the wild rabbit. All the colors of today’s rabbit breeds came about through mutations and combination breeding. Two pigments, black-brown eumelanin, and reddish-yellow phaeomelanin add color to mammalian fur, including human hair.
Crossbreeding attempts were used to get to the bottom of the color inheritance of rabbits. The hereditary symbols of the genes (see box for technical terms) go back to the zoologist Hans Nachtsheim (1890 – 1979); they differ from the internationally used ones but are used in the German-language books. For this reason, we adopt them here as well.
A rabbit the color of the wild rabbit carries the gene designation ABCDG. The capital letters symbolize dominant gene variants. The corresponding recessive variants are written with small letters. Since genes come in two copies, one from the father and one from the mother, the correct formula should be ABCDG/ABCDG. For the sake of simplicity, the simple formula is written for homozygous animals.
Mendel’s Rules
In the 19th century, the monk Gregor Johann Mendel carried out systematic crossbreeding experiments on plants and thereby discovered important rules of heredity. Even today, when DNA analyzes are commonplace, Mendel’s theory of heredity is practical. To understand them, you have to know that body cells contain a double set of chromosomes, while egg cells and sperm only have a single set. During fertilization, the egg and sperm fuse, creating a double set of chromosomes. So the genes are mixed up again and again.
As an example of the so-called dominant-recessive inheritance, we choose Alaska ABCDg and Havana ABcDg. Alaska and Havana differ in one color gene: Factor C stands for the basic color black, c for Havana brown. Both colors are based on eumelanin, the difference lies in the fine structure of the color granules: the brown ones are smaller, oval, and less densely packed with pigments than the black ones. G is the factor for wild color, g stands for solid color rabbits, as both breeds are.
In the first generation (F1), the crossbreeds are all the same. This is the first Mendelian rule, the law of uniformity. The homozygous parents each pass on a C or a-c to the boys, so that they all carry Cc. The capital C is dominant over the c, so the boys are all black, although they also carry Havana in their genetic makeup. Her phenotype, i.e. her appearance, is black, while the genotype, her genetic makeup, is black and Havana Cc. So you don’t always see the colors of the rabbits!
The next generation, the F2, will be interesting. F1 animals can each pass on either a C or a c. In a sibling pairing, the boys split up (Mendel’s second rule, law of splitting): 25% are homozygous black, 25% homozygous Havana, 50% homozygous black (see table above).
Sable Rabbits Shear Out
In addition to the dominant-recessive inheritance, the intermediate inheritance is also known. Here the phenotype of the F1, i.e. the external appearance, does not correspond to either of the parents but is optically a mixture. The breeders of sable rabbits know this. The type marten, as required by the standard, is split inbreeding, there are almost black dark martens and Russian-colored animals.
A stands for the full color in the gene formula, a for albino. The marten is a partial albino with the designation am. The homozygous form aim is almost black. Only in the split form aman does the well-known marten color (type marten) appear. If you cross two types of martens a man, you get 25% dark martens am, 50% type martens, and 25% Russians anan. If you cross dark marten times Russian, you get 100% type marten
G is the wildness factor. A complicated signaling pathway ensures that the individual hairs are banded by alternately storing eumelanin and phaeomelanin in the hair. G also leads to the typical wild color characteristics of light belly, light border of nose and jawbone, the light underside of flowers, brownish neck wedge. The wildness factor has three mutation levels. The tan coloration goes is between G wild and g monochromatic. Here the banding of the hair has been removed, but the wild color markings are still present.
D is a dilution factor, the pigments are stored less densely in the recessive variant d. Black ABCDg becomes blue ABCdg, Havana ABcDg becomes mauve ABcdg.