(单词翻译:单击)
From a tiger's stripes, to a jaguar's rosettes, to a tabby's whorls, cats come in lots of different colors and patterns.
从老虎的条纹，到美洲虎的玫瑰花结，再到虎斑猫的螺纹，猫有各种各样的颜色和纹路。
Normally, we imagine that the way an animal looks is inherited from its parents — basic genetics stuff.
通常情况下，我们会认为动物的外貌遗传于它们的父母——也就是遗传因素。
But sometimes, the origin isn't so simple. Like, the coloring of some domestic cats is tied to their sex.
但是有时并没有那么简单。比如，一些家猫的颜色与它们的性别有关。
That's why orange cats are much more likely to be males, and calicos and torties are almost always female.
所以橘猫更有可能是雄性，而三色猫和玳瑁猫几乎总会是雌性。
But Siamese cats are especially interesting — because their recognizable coloration is actually dependent on temperature.
但是暹罗猫尤为有趣——因为它们可识别的颜色实际上取决于温度。
Animals get their dark color because their bodies produce melanin.
动物之所以有深色是因为它们的身体会产生黑色素。
Melanin is the same protein responsible for variation in human skin tone and making you tan.
黑色素是一种蛋白质，它也可以改变人类的肤色，让你变黑。
And it's produced thanks in part to the enzyme tyrosinase. Normally, this enzyme does its job pretty well.
它的产生部分归功于酪氨酸酶。正常情况下，这种酶的工作做得很好。
But in some breeds of mouse, rabbit, and cat — and even in some human cases — the enzyme doesn't quite work the same.
但在某些品种的老鼠、兔子和猫身上——甚至在某些人类身上——这种酶没有做好它的工作。
In particular, virtually all Siamese cats have a mutated version of the gene that codes for this enzyme.
尤其是，几乎所有暹罗猫一种突变基因，这种基因可以编码这种酶。
So their tyrosinase is extremely sensitive to temperature.
所以它们的酪氨酸酶对温度极其敏感。
So sensitive, in fact, that it unfolds and no longer functions at the average cat body temperature, around 38 degrees Celsius.
事实上，它非常敏感，以至于在猫的平均体温，约38摄氏度下，它就不能正常工作了。
That isn't great for the enzyme - can't really do its job anymore - but it does give the cats their adorable coloration.
这对酶来说可不妙—没再也无法完成它的工作-但它却给了猫猫讨喜的颜色。
Without functional tyrosinase, no melanin gets produced, so most of the animal's fur is a creamy white: It's essentially albino.
没有了功能性的酪氨酸酶，就无法产生黑色素，所以大部分动物的皮毛是乳白的：其本质是白化。
But! Siamese cats also have those super cute boots and that little brown mask.
但是！暹罗猫也有超级可爱的靴子和那种棕色的小面具。
And that's because tyrosinase is functional in their extremities, like their tails, legs, noses, and ears.
那是因为酪氨酸酶在它们的四肢，比如尾巴、腿、鼻子和耳朵上能起作用。
Compared to their volume, these parts of the body have a larger surface area for heat to escape from,
和它们的体积相比，身体的这些部分有更大的表面积来释放热量，
so these small and slender body parts lose heat more quickly than the cat's central core.
所以这些小而纤细的身体部位比猫的核心部位散热更快。
This is just like how your fingers and feet and nose are the first things to get cold when you step outside.
这就像是，当你站在外边时，你的指尖、脚和鼻子能够首先感觉到冰冷。
Or how a narrow icicle is going to melt before a compact ice cube made of the same volume of water.
或者像是，一个狭窄的冰柱如何在一个由相同体积的水组成的密集冰前融化。
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.
在猫身上，这意味着它们的脸、四肢和尾巴，只比身体其他部分低几度而已。
And that difference is enough to preserve delicate tyrosinase's shape and function, allowing it to color the fur.
这种差异足以保持微妙的酪氨酸酶的形状和功能，让它给皮毛上色。
If you ever get to see a newborn Siamese kitten, you can actually watch this process happen live.
如果你见过刚出生的暹罗猫宝宝，你可以亲眼目睹这个过程。
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.
猫猫刚出生的时候，它们从头到尾都是白色的，因为子宫恒温在38摄氏度左右。
Out in the world, though, the temperature around the kitten is cooler than its body,
然而在外面的世界里，小猫周围的温度比它身体的温度要低，
so it loses heat to the environment — especially from its tiny toes and tail.
所以它把热量发散到了环境中——尤其是它的小脚趾和尾巴上的温度。
Within a few weeks, the characteristic Siamese color pattern starts to emerge as new fur grows
几周后，随着新皮毛的生长和酪氨酸酶在猫的四肢发挥作用，
and tyrosinase gets to work in the cat's extremities. So unless you're keeping mittens on your kittens,
典型的暹罗颜色开始出现。所以，除非你给小猫戴上连指手套，
Siamese cats will develop their trademark coloration all thanks to this delightful mutation.
否则暹罗猫会因为这种可爱的变异而发育出它们标志性的颜色。
Thanks for watching this episode of SciShow! And special thanks to our patrons on Patreon —
感谢收看本期节目！特别感谢我们的赞助人——
especially everyone who keeps sharing their amazing animal photos in the floofs channel on our Discord. We love them so much .
尤其是那些不断在Discord频道和我们分享可爱动物图片的每一位。我们非常喜欢。
If you want to join in the fun and help us keep making educational videos like this, we would love to have you.
如果你想加入我们，帮助我们制作像这样有教育意义的视频，欢迎大家的加入。
You can learn more at patreon.com/scishow. And maybe we'll see you in the Discord!
大家可以登陆patreon.com/scishow了解更多。我们在Discord栏目见！
