In two new studies published in Current Biology, researchers from Stanford University and Kyushu University found that ginger cats have an elusive genetic mutation that gives orange cats their vibrant colour – a mutation found in no other mammal.
Researchers compared DNA samples from dozens of cats with and without orange fur and found that ginger cats are missing a small section of DNA in a gene called ARHGAP36. This gene controls the production of pigments in the cat's skin, fur, and eyes. Without this piece of DNA, the gene becomes more active, resulting in the lighter orange colouring associated with ginger cats.
"In a number of species that have yellow or orange pigment, those mutations almost exclusively occur in one of two genes, and neither of those genes are sex-linked," lead author of the study and senior scientist in genetics, Christopher Kaelin said in a statement.
In cats without orange colouring, this gene is regulated to limit pigment intensity. But in ginger cats, the missing DNA means the gene goes unchecked, leading to the production of lighter, orange-toned pigments and could be linked to other health conditions.
"It's a genetic exception that was noticed over a hundred years ago," Kaelin said. "It's really that comparative genetic puzzle that motivated our interest in sex-linked orange."
Scientists observed that ginger cats are overwhelmingly male with the genetic mutation – dubbed sex-linked orange – revealing that the pigment-related gene sits on the X chromosome, of which male cats have only one (paired with a Y chromosome). So, a single missing DNA segment is enough to give a male cat its full ginger coat.
Females, on the other hand, have two X chromosomes. For them to be fully orange, both chromosomes would need to have the same missing DNA, which is much rarer. As a result, female ginger cats are less common and are more likely to display tortoiseshell or calico patterns instead.
"We think it's an example of how genes acquire new functions that allow for adaptation," said Kaelin.
For orange cats, their widespread presence might be a result of human preference. Centuries ago, the rare orange, calico, or tortoiseshell cats likely caught the eye of humans, who then promoted their breeding. Today, orange cats are found across the globe.
"This is something that arose in the domestic cat, probably early on in the domestication process," Kaelin said. "We know that because there are paintings that date to the 12th century where you see clear images of calico cats. So, the mutation is quite old."
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