Orange cats have long been known for their playful and mischievous personalities. In Italy, there’s even a saying that the red cat is always the leader.
This reputation might have something to do with the fact that most orange cats are male—a phenomenon that has puzzled scientists until recently. Two independent research teams have now uncovered the genetic secret behind the orange coat in domestic cats.
According to Smithsonian Magazine, both teams reached the same conclusion: a mutation on the X chromosome.
In male cats, which have one X and one Y chromosome, a single mutated X chromosome is enough to produce an orange coat. Female cats, on the other hand, have two X chromosomes. This explains why female cats with orange fur often exhibit mixed patterns, such as the black-and-orange markings of tortoiseshell cats or the tri-colored coats of calicos.
Kelly McGowan, a geneticist at Stanford University who participated in one of the studies, noted that cats are a unique case compared to other animals like dogs, sheep, and horses when it comes to orange coloration.
“Our work provides an explanation for why orange cats are a genetic unicorn of sorts,” McGowan told Newsweek.
In most mammals, a protein called Mc1r is responsible for red or orange pigmentation. But in cats, researchers discovered that the gene Arhgap36 plays a pivotal role. This gene, located on the X chromosome, codes for a protein that regulates embryonic development—a vital function that makes it an unlikely spot for an aesthetic mutation.
Greg Barsh, a geneticist from Stanford University, and his team found that a mutation in the Arhgap36 gene causes a 13-fold increase in RNA production, which affects pigment in melanocytes, the skin cells responsible for hair color. Interestingly, this mutation involves a small piece of missing DNA from the Arhgap36 gene, limiting its effect to hair pigmentation without interfering with the gene’s critical developmental roles.
In females, the presence of a normal Arhgap36 gene on the second X chromosome typically balances out the mutation, leading to mixed coat patterns. But for males, who inherit only one X chromosome from their mothers, the mutation’s influence on fur color goes unopposed.
This discovery marks the first time pigmentation in animals has been linked to this genetic pathway.
Hiroyuki Sasaki of Kyushu University in Japan, who was involved in the research, told Newsweek, “An obvious next question is when and where this genetic variation arose and how it spread, as our work showed that this mutation is common in orange cats worldwide.”