Scientists have finally uncovered the secret behind why some cats have that beautiful orange fur.
In a recent study, researchers at Stanford Medicine identified a unique genetic mutation that makes orange cats orange—and interestingly, it’s found in no other mammal.
This discovery helps explain how certain genes can create new traits and adds to our understanding of animal coloration.
The gene responsible is called Arhgap36, which, until now, was only linked to neuroendocrine tissues in other animals.
Researchers had been studying this gene for its role in cancer and developmental biology, never suspecting it had anything to do with fur color.
But as it turns out, Arhgap36 is unusually active in the pigment cells of orange cats—something not seen in non-orange cats, humans, or even mice.
According to lead researcher Christopher Kaelin, this is an incredibly rare case of a gene being “misexpressed” in a specific cell type.
Normally, Arhgap36 isn’t involved in pigment production, but in orange cats, it activates in the cells responsible for their coat color. This change disrupts the usual pathway for producing pigment, leading to their signature ginger fur.
The mutation is sex-linked, appearing on the X chromosome. This means that it’s much more common for male cats to be fully orange. Male cats only have one X chromosome (XY), so if they inherit the mutation, they’re entirely orange.
Females, on the other hand, have two X chromosomes (XX), so they need the mutation on both chromosomes to be fully orange—a much less likely scenario.
Most female orange cats end up with patches of orange and black, resulting in what we call tortoiseshell or calico patterns. This happens because of a process called random X inactivation, where one of the X chromosomes in each cell is switched off, leading to a mosaic of colors.
The scientists also discovered that Arhgap36 is not expressed in other tissues like the heart, brain, kidneys, or adrenal glands of orange cats. This means the gene’s effect is purely cosmetic—just fur color and nothing more.
Though some people think orange cats are friendlier or more mischievous, Kaelin suggests this may simply be because most of them are male, and male cats often have different behaviors than females.
Interestingly, the mutation that turns cats orange is ancient. Paintings dating back to the 12th century show calico cats, suggesting the trait emerged early in domesticated cats. Over time, humans may have favored these brightly colored cats, leading to their spread around the world.
The discovery is significant not just for cat lovers but also for scientists studying how animals evolve. Kaelin believes this mutation is a perfect example of how genes can adapt to create new traits. His team is now exploring how other animals, like tigers, cheetahs, and even golden retrievers, develop their own distinctive colors and patterns.
This finding is a big step forward in understanding the genetics of animal coloration and may even unlock more secrets about how new traits evolve over time.
