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  • 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 parentsbasic

  • 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 interestingbecause 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 catand even in some human casesthe

  • 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 Patreonespecially 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

  • And maybe we'll see you in the Discord!

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シャム猫に潜む愉快な異変 (The Delightful Mutation Behind Siamese Cats)

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    林宜悉 に公開 2021 年 01 月 14 日