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Today, I'd like to talk about why Calico cats have that mix of orange, black and white fur, and why they're usually female.
After more than 60 years, scientists in Japan finally found the answer.
Hi everyone, this is SCIEN-SPOT, the podcast that shines a light on the latest science and technology from Japan.
I'm your host, REN from SCIEN-TALK.
You've probably seen Calico cats before, cute little ones with orange, black and white patches.
But have you ever noticed that they're almost always female?
Male Calico cats are super rare.
Why is that?
And why do their coats look like little patchwork quilts?
It all comes down to genes and something called X-chromosome inactivation.
Like humans, cats have sex chromosomes.
Females have two X-chromosomes, XX.
Males have one X and one Y, XY.
The gene that decides orange and black fur is found on the X-chromosome.
Now here's where it gets cool.
In female cats, every cell picks one of the two X-chromosomes to turn off.
It's random.
Some cells turn off the X from mom, others from dad.
This is called X-chromosome inactivation.
It was first suggested in 1961.
If one X has the orange version of the gene and the other has the black version.
This on-off process leads to patches, some with orange, some with black.
It's like nature's mosaic.
But until now, scientists didn't actually know what the orange gene really was.
They knew it was there, but didn't know how it worked or why it behaved that way.
Researchers from Kyushu University and other groups in Japan decided to dig deeper.
They worked with cat owners in Fukuoka and studied the DNA of cats with different fur colors.
They focused on the section of the X-chromosome where the orange gene was believed to be.
And they found a tiny missing part of DNA about 5,000 liters long and a gene called ALHGAP36.
This deletion was only found in cats with orange fur.
Cats without orange didn't have it.
To double-check, they looked at over 50 more cats or international data,
and the pattern held if a cat had the deletion, it had orange fur.
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If not, it didn't.
That's strong evidence this small deletion causes the orange color.
But how?
They looked at skin from orange fur areas.
In these areas, the ALHGAP36 gene was more active than normal.
This high activity stopped the gene for black pigment from working well and instead triggered the orange pigment.
So basically, the missing DNA acts like a broken brake.
With no brake, ALHGAP36 goes wild and turns on the orange coloring.
They also checked how this related to X inactivation.
They looked at a marker called DNA methylation, sort of a stitch that shows if a gene is on or off.
In female cats, ALHGAP36 was turned off in some cells and on in others, matching what we'd expect from X inactivation.
So now we know, if the X chromosome with deletion is on, orange patch.
If the one without it is on, black patch.
What about this? Those are from areas where pigment cells didn't grow at all.
It's like a patchwork occurred, but each square is a random decision made in a tiny cell.
To sum it up, researchers found that a small deletion in the ALHGAP36 gene causes orange fur in calico cats.
And the mix of orange and black comes from X inactivation, each cell randomly choosing which gene to use.
After more than 60 years of guessing, we finally understand why calico cats look the way they do.
Fun fact, this research was partly funded through crowdfunding by Kyushu University.
And this is, I think, pretty amazing.
Their paper was just published in the journal Current Biology.
That's it for today's SciencePod.
How did you like the story of calico cats and their calico coats?
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And see you tomorrow!
