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It's easy to assume a cat's coat pattern is based exclusively on genetics, but that isn't entirely the case for Siamese cats. Their unique coloration comes from a combination of genetics, a fragile enzyme, and losing heat from little noses and toe beans.

Hosted by: Hank Green

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[ ♪INTRO ].

From a tiger's stripes, to a jaguar's rosettes, to a tabby's whorls, cats come in lots of different colors and patterns. Normally, we imagine that the way an animal looks is inherited from its parents — basic genetics stuff.

But sometimes, the origin isn't so simple. Like, the coloring of some domestic cats is tied to their sex. That's why orange cats are much more likely to be males, and calicos and torties are almost always female.

But Siamese cats are especially interesting — because their recognizable coloration is actually dependent on temperature. Animals get their dark color because their bodies produce melanin. Melanin is the same protein responsible for variation in human skin tone and making you tan.

And it's produced thanks in part to the enzyme tyrosinase. Normally, this enzyme does its job pretty well. But in some breeds of mouse, rabbit, and cat — and even in some human cases — the enzyme doesn't quite work the same.

In particular, virtually all Siamese cats have a mutated version of the gene that codes for this enzyme. So their tyrosinase is extremely sensitive to temperature. So sensitive, in fact, that it unfolds and no longer functions at the average cat body temperature, around 38 degrees Celsius.

That isn't great for the enzyme - can't really do its job anymore - but it does give the cats their adorable coloration. Without functional tyrosinase, no melanin gets produced, so most of the animal's fur is a creamy white: It's essentially albino. But!

Siamese cats also have those super cute boots and that little brown mask. And that's because tyrosinase is functional in their extremities, like their tails, legs, noses, and ears. Compared to their volume, these parts of the body have a larger surface area for heat to escape from, so these small and slender body parts lose heat more quickly than the cat's central core.

This is just like how your fingers and feet and nose are the first things to get cold when you step outside. Or how a narrow icicle is going to melt before a compact ice cube made of the same volume of water. In a cat, this means the face, limbs, and tail are just a few degrees cooler compared to the rest of the animal's body.

And that difference is enough to preserve delicate tyrosinase's shape and function, allowing it to color the fur. If you ever get to see a newborn Siamese kitten, you can actually watch this process happen live. When the cats are born, they're totally white, since the inside of the womb is a uniform and toasty 38 degrees Celsius or so.

Out in the world, though, the temperature around the kitten is cooler than its body, so it loses heat to the environment — /especially/ from its tiny toes and tail. Within a few weeks, the characteristic Siamese color pattern starts to emerge as new fur grows and tyrosinase gets to work in the cat's extremities. So unless you're keeping mittens on your kittens, Siamese cats will develop their trademark coloration all thanks to this delightful mutation.

Thanks for watching this episode of SciShow! And special thanks to our patrons on Patreon — especially everyone who keeps sharing their amazing animal photos in the floofs channel on our Discord. We love them so much .

If you want to join in the fun and help us keep making educational videos like this, we would love to have you. You can learn more at patreon.com/scishow. And maybe we'll see you in the Discord! [ ♪OUTRO ].