At one time, cat breeders assumed that by adding two cats together, they would know what kittens would be produced and were most of the time shocked by the results. This was because the thinking was that the color of a cat's coat was dictated by a single gene but modern developments in genetic testing has shown that there are actually three genes that work together to produce the final coat color and pattern.
Blotches and stripes
Using the tabby cat as an example, there are four main variations of the tabby pattern; the stripes, spotted, ticked and blotched. Each of these patterns is caused by the genes the cat receives from its parents. One gene says whether a cat will be striped or blotched while another can turn those stripes into spots. This means if the cat doesn't have the spot causing gene, it will remain with stripes.
To use another example given by The Tech: if you have a wall which is painted red and you then paint it with red stripes, it will remain red. However if you have a black and red striped wall and paint red stripes in the opposite direction, you will get black spots. So going back to tabby patterns, the blotched cat is the red wall and another spot gene is another pot of red paint. But if you add the spot gene to the striped cat, you get spots just as you did with the black and red striped wall.
One gene or two?
Cats like people receive two copies of each gene, one from each parent so this means that there are different combinations available in siblings. Using the striped and blotched example there are three possibilities: striped/striped, blotched/blotched and striped/blotched.
Now which of these genes is the dominant? In genetics, this refers to a gene that is stronger than another gene and therefore is considered the dominant. In this scenario, the striped is the dominant gene so in the combination of striped/blotched, the cat will be striped as it is the dominant gene.
Predicting kittens
Armed with this knowledge cat breeders began to be able to predict what kitten would come from a certain pairing of cats. While the combination will have random results, so there is no way of predicting that the third kitten born will be a certain pattern, it does allow them work out the general ratios of kittens involved. For example, with the striped/blotched pairing, there is a ratio of 3:1 meaning that three out of every four kittens will be striped and just one will be blotched.
Gene codes
Away from the tabby pattern, geneticists have managed to recognize a range of genes that lead to different colors and patterns in different cat breeds. Here are a few of the major ones:
The gene code C refers to an enzyme called tyrosine that is the first step in pigment production. When it is recessive, it causes albinism in cats and also what is called temperature sensitive albinos. This results in colors such as Siamese and Burmese and is also known as the Colorpoint pattern. It results in dark color hair at the coolest points of the body such as the tail, legs, face and ears while the warmer parts of the body are a lighter shade
The gene code W is known as the white masking gene and stops cells producing normal pigmentation. This creates cats such as pure white cats and solid and white patterns.
The gene code S is called the white spotting or piebald spotting and creates pattern such as the white blaze across the face, a white bib, the tuxedo pattern or dappled paws. It is also the reason for the mitten pattern found in breeds such as the Birman and the Snowshoe.
When a cat has the red gene (O) the black color (eumelanin) in the coat is replaced with red (phaeomelanin). It is located on the X chromosome so male cats only have one version of this gene, resulting in red fur when it is dominant and non-orange fur when recessive. Female cats get two versions of the gene so when one parents has O dominant and the other o recessive (Oo), the result is a tortoiseshell cat with some red areas and some non-red areas.
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