Have you ever wondered why your cat’s coat looks the way it does? Wonder no longer! Earlier this month, Emily Summerbell, a PhD student at Emory University, tweeted a ‘tweetorial’ on cat coat genetics. I used it to figure out the underlying genetics for my own cat’s coat.

This is my cat ‘Little Excuse’ (because when he’s sleeping on your lap, you’ve got an excuse to not get up). 

Excuse has a short coat, which is controlled by the FGF5 gene. Short hair (L) is the dominant trait, meaning that if one out of two copies, or alleles, of the gene encodes for short hair, the cat will end up with short hair. Excuse is either homozygous, meaning he has two short hair alleles (LL), or heterozygous, meaning he has one short hair, and one long hair allele (Ll).

Though Excuse is for the majority white (we’ll get back to that later), he generally has dark-colored fur. This is encoded by the TYRP1 gene, for which the black allele is dominant. If he would have the allele for orange hair, this would override the black color, so the lack of any orange means that he has the recessive allele for the orange gene.

Back to the white fur. White fur is caused by the KIT gene, but it is not all-or-nothing. As you can see, Excuse is more than 50% white, which indicates that he is probably homozygous for the dominant white gene (SS). 

Lastly, although it’s not clearly visible in this picture, Excuse’s dark patches have a tabby pattern to them. This is caused by the agouti and tabby genes, where the agouti gene determines whether a cat has a solid color coat, and the tabby gene determines the exact pattern.

Emily goes into much more detail in her Twitter thread, explaining colorpoint coat patterns, cats with diluted colors and more. If you are wondering why your cat looks the way it does, this thread will tell you all you need to know.

But in the meantime, what colour is your cat's coat — and do you know why?