Orange cats have won a reputation for being energetic rascals. In Italy, it’s said the red cat is always the leader.
That’s probably because red/orange cats are almost always males, and now we know why thanks to two teams of scientists probing the genetic lineage of the orange coat in domesticated felines.
Working separately,, reports Smithsonian Magazine, the two teams have independently arrived at the same conclusion—a mutation on the X chromosome.
Male animals have one copy of the X chromosome, while females have two—explaining yet further why female cats with orange in their coats tend to have it mixed in with other colors such as black in the case of a ‘tortoiseshell cat,’ and white in the case of a calico.
Kelly McGowan, a Stanford University geneticist who participated in one of the two studies, said that cats are a “fascinating exception” to the trend of orange coloration in other animals such as dogs, sheep, horses, and rabbits.
“Our work provides an explanation for why orange cats are a genetic unicorn of sorts,” she told Newsweek.
In most other mammals, mutations in a protein called Mc1r lead to red hair color, but not in cats. Instead, this decades-long mystery has been solved with the identification of the gene Arhgap36 that codes for a protein along the X chromosome.
Arhgap36 has never been suspected as a potential candidate for the “orange gene” before, in part because the protein it codes for regulates embryonic development—a life-or-death function, and not a place one would image to look for an asthetic mutation.
Greg Barsh from the Stanford University team that included McGowan found that the Arhgap36 mutation in orange cats resulted in 13-fold increase in the production of RNA, the molecule that reads genetic material contained in DNA.
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Furthermore, they found that rather than being a dangerous mutation, the orange cats had just a sliver of DNA missing from the Arhgap36 gene, and that this absense meant it’s effects were seen only in melanocytes, or skin cells that produce hair color.
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The Arhgap36 was found on the X chromosome. Females inhereit a copy of the X chromosome from both parents, meaning that the influence of a mutated copy of Arhgap36 is almost always balanced out by the normal copy inherited from the other parent.
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By contrast, male cats have just one X chromosome—from their mother. If they receive a mutated Arhgap36, there will be no other influence on the cat’s fur color from the father’s side.
It’s the first time in animals that pigment production has been identified through this pathway.
Hiroyuki Sasaki from Japan’s Kyushu University told Newsweek “an obvious next question is when and where the genetic variation arose and how it spread, as our work showed that this variation is common in cats with orange coloration worldwide.”
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