Name: 為什麼柯基犬混血兒總是長得像柯基犬？ (Why Do Corgi Mixes Always Look Like Corgis?)
Uploaded: 2021-01-14T10:27:35.000Z
Duration: 4 min 33 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

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You might have noticed that a lot of corgi mixes look exactly like…

a corgi in a costume of a different dog breed.

No matter what, though, something about these pups always screams “corgi.”

It's the stumpy legs that gives them away.

Those legs aren't just a coincidence, though.

They're actually the product of thousands of years of breeding.

And those little legs come from a funky mutant gene

And purebred corgis have been bred to make sure that trait gets passed on every time.

But when corgis breed with other dogs, their pups often have those same

little legs, because that gene is dominant

so even if a dog has only one copy of the gene, short legs will win out.

In corgis, dwarfism isn't caused by any old gene.

It's caused by a mutant gene called a retrogene.

A retrogene forms when the usual system for building proteins

In a normal case, a gene, made of DNA, is transcribed into a molecule

The cell then interprets that code and uses it as an instruction manual

which is only supposed to act as a messenger

that converted DNA manages to slip back into the genome—in a different place.

Usually that gene doesn't do anything; it just sits there.

that duplicated gene can even produce proteins.

That's exactly what's happening with the short-legged dog imposters.

Multiple genes can cause dwarfism in dogs, but in corgis, and corgi mixes,

Specifically, there are multiple retrogenes derived from a gene called FGF4.

It codes for a type of protein called a growth factor

And that's a normal gene that all dogs have on chromosome 18.

But it's become a retrogene and copied itself back into the genome -- more than once.

There's one of these retrogenes on chromosome 12, and one on chromosome 18.

Either one is enough to cause dwarfism in dogs.

But some really stumpy breeds -- like corgis and dachshunds -- have both.

Scientists think that the expression of these extra growth factors

In fact, similar genetic changes are linked with dwarfism in humans.

In short-legged dogs, the extra FGF4 tells limbs to stop growing early,

and you end up with a regular-sized dog with stubby legs.

And many breeds, from Pekingese to basset hounds, have short legs for similar reasons!

One, this mutation appeared a really long time ago,

back in the early days of domesticating dogs.

And two, humans throughout history have found this trait so attractive

that they bred these waddly dogs into existence all around the world.

The cuteness is not without its downsides, though.

The same retrogene that gives dogs their adorable waddle

is also linked with spinal disease that can cause pain and neurological damage,

which scientists are still trying to understand.

So next time you see one of those dogs in a corgi-shaped package,

remember it's because humans have a soft spot for those little, furry mutants

and probably have ever since our long friendship with dogs began.

Now that you've had your dose of cute internet dogs,

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