Thanks to Brilliant for supporting this episode of SciShow.

If you’re looking to grow your STEM skills this year, head Brilliant.org/SciShow and check out their new Logic Course! [ ♩ INTRO♩ ] Have you ever noticed how rarely you see a brown cat? The genetics of cat color are fairly complicated, as you might guess.

But not only is it possible for brown cats to exist – under the right circumstances, a cat can actually change color. We regularly see brownish looking tabbies out in the world, but truly brown cats are fairly rare. Melanin is the pigment that adds color to the coat and skin of cats, just like in humans.

And it comes in different types. Eumelanin specifically makes dark brown to black pigments. So eumelanin is really key in making a black cat black.

And this black pigment production is thanks to a specific gene responsible for an enzyme called tyrosinase-related protein 1, or TYRP1 for short. This enzyme is responsible for converting the amino acid tyrosine into eumelanin. Amino acids are the basic building blocks of proteins, but they’re also used to create many other things within the cell.

So when a protein is digested and broken down into its component amino acids, the cell can snag some tyrosine and turn it into pigment. Cats only need to get one correctly working copy of TYRP1 from their parents to give them a black coat, meaning the allele for black coat color is dominant. But there are actually a couple recessive versions of that coat gene as well.

Depending on which variant of that gene a cat has, different color variations show up instead of black. One possible genetic mutation messes with TYRP1 in a way that actually seems to produce lighter eumelanin. Which means you get a brown cat!

In other cats, a different mutation loses some use of its ability to produce sufficient eumelanin altogether. So cats with this particular recessive trait end up with a reddish cinnamon color, produced by other red pigments, instead of black or brown. Strangely, there’s a way to change the color of a cat’s coat, even if it has the dominant black coat color allele.

Before we get any farther, don’t try this at home. Always follow your vet’s recommendations for feeding dear sweet Mittens. In one extensive experiment testing dietary impacts on black cats, veterinary researchers gave cats and kittens food with varying levels of tyrosine as well as phenylalanine, another amino acid.

And by controlling the quantities of amino acids in their grub, the researchers were able to take kittens born with black coats and turn them reddish brown in only 3 months! In the case of the adult cats, not only did they turn brown, but it also resulted in pregnant black-turned-brown cats giving birth to brown kittens! Because they didn’t have enough tyrosine for the little ones’ coats, never mind their own.

These experiments helped to demonstrate the importance of dietary tyrosine. Since TYRP1 needs it to make eumelanin, a cat will slowly turn from black to a reddish brown if it doesn't have enough. And it looks like phenylalanine plays a role as well, since not having enough of this amino acid was also shown to mess with the black pigmentation levels.

This is likely because cells can change it into tyrosine, acting as an additional source of the eumelanin-producing amino acid. And for all these cases of food-induced color change in cats and kittens, the black color can be restored if they’re fed a more complete diet. It just takes a little while since they have to shed and replace all their fur.

So if a brown cat ever crossed your path, its unique coat is likely thanks to its recessive genes. But there is still a slight chance that it’s a black cat after all! But if you’d like to counteract that bad luck, you might like to try learning something new like with a course from Brilliant.

For example, their interactive Logic course. What’s great about Brilliant is that you learn why subjects like logic are important in the first place, which makes you want to understand it on a deeper level than just memorizing rules for their own sake. And Brilliant is always making their courses more interactive, to keep you engaged as you learn.

If you’re interested, you can go to brilliant.org/scishow to save 20% off an annual premium subscription to Brilliant. [♩ OUTRO♩ ]