In the first article in this series, we learned that there are eight different fur colors in domestic cats. Recall that the eight colors are: black and its dilute version blue (which we see as grey), chocolate and its dilute lilac, cinnamon and its dilute fawn, and red (seen as orange) and its dilute cream. These colors can be modified based on the genes for features such as tabby patterns, white fur, points, and shading.
Now let's take a look at the genetics behind the eight colors, to get a better understanding of how fur color in cats is determined, and why some colors are more common than others.
The black gene
The first gene controls the production of the black-colored pigment eumelanin. Known as the B gene or the B locus, this gene comes in three flavors referred to as alleles. You may remember from grade school genetics that each parent contributes one allele, and different allele pairs produce different physical traits or characteristics. The traditional pea plant examples illustrated the scenario for a gene with two alleles, but genes can have three or more alleles.
The B allele produces black fur, the b allele creates chocolate fur, and the b' allele results in cinnamon fur. The B allele is dominant, meaning that if a kitten receives a B allele from either parent, it has a base color of black. (This color can still be modified by other genes, but all cats start with either black, chocolate or cinnamon.)
The b' allele is recessive, so any kitten who receives copies of this allele from both parents is genetically coded for cinnamon as its base color. No other combination of the B, b' and b alleles gives rise to cinnamon.
The b allele is intermediate to the other two. It is dominant to the b' allele, but recessive to the B allele. This is where the black gene differs from the classroom examples. Instead of only four possible combinations of two different alleles, we have nine ways the three alleles can combine in pairs:
BB – Black
Bb – Black (B is dominant)
Bb' – Black (B is dominant)
bB – Black (B is dominant)
bb – Chocolate
bb' – Chocolate (b is dominant over b')
b'B – Black (B is dominant)
b'b – Chocolate (b is dominant over b')
b'b' – Cinnamon
While black cats are well-known and commonly seen as pets and in shelters, chocolate and cinnamon cats are more rare. Cat shows present an excellent opportunity to view cats of many colors and breeds.
In part 2 of this article we will learn about the genetics of red/orange fur, and how this gene interacts with the gene for black-based colors.