Chocolate and cinnamon coat colours

The coat colours chocolate and cinnamon are caused by mutations in the gene TYRP1 (tyrosinase-related protein 1) which is involved in the production of the black colour pigment eumelanin. This gene locus is called B-locus. The brown variants show a suggested allelic series, with the following dominance pattern: B > b > b1.

The B allele is dominant and represents the normal the wild type black coat colour. Cats with brown genotypes bb or bb1 have a chocolate phenotype, whereas cats with the light brown genotype b1b1 have a cinnamon phenotype, independent of B and b alleles.

How can the different genotypes for the colours chocolate and cinnamon and the Siamese and Burmese patterns be identified ?

Recently, the mutations leading to the different coat colours have been found in the USA, thus permitting the development of a genetic test for each of the colours. After validating these tests in collaboration with several german veterinarians and cat breeders, Laboklin can now offer the tests to all interested breeders. For the coat colour chocolate, Laboklin tests the four most important gene loci, therefore ensuring a very reliable test. For the coat colour cinnamon as well as the Siamese and Burmese coat patterns, only one mutation has been published to be responsible for the corresponding colour.

How does the genetic test work and how safe is it?

Firstly, the DNA which is the genetic information of an animal is isolated from a blood or a cheek swab sample. Then the genes of interest are amplified a million-fold by PCR (polymerase chain reaction) to facilitate the following analysis. The analysis is automatically performed by a genetic analyzer and reveals the gene sequence of the region of interest.

Therefore, the mutations leading to the different coat colours can be seen directly and heterozygous carriers of these mutations can also be identified. Since the test is done mainly automatically, laboratory errors can be widely excluded.

Interpretation of the test results

The test results will be submitted separately for each coat colour, so that the genotype for each corresponding gene locus will be given.

Test results exemplary for cinnamon:

Genotype BB: the cat is homozygous for the wild type allele. The cat does not carry cinnamon and will not pass it onto its offspring.

Genotype Bb1: the cat is heterozygous for the cinnamon allele. The cat carries cinnamon and can pass the gene onto its offspring with a probability of 50%.

Genotype b1b1: the cat is homozygous for the cinnamon allele. The cat will phenotypically show cinnamon coat colour (maybe in diluted form as fawn) and will pass the

gene onto its offspring with a probability of 100%.