08/01/2025
Finally
In a genetic breakthrough that took 60 years, scientists finally discovered what causes orange fur in cats.
They also found what makes the patchy patterns of calicos and tortoiseshells.
Two independent research teams discovered that a genetic deletion near a gene called Arhgap36, located on the X chromosome, drives the production of orange pigment in feline fur. This breakthrough sheds light on the long-standing genetic mystery that explains why most orange cats are male and why nearly all calicos and tortoiseshells are female.
The researchers found that this deletion increases the production of Arhgap36 RNA, activating a molecular pathway that causes melanocytes—pigment-producing skin cells—to generate a reddish-yellow pigment. This mechanism bypasses the more commonly known Mc1r gene, which influences red hair in other mammals but doesn’t explain orange fur in cats.
The discovery, published on the preprint server bioRxiv, marks the first time Arhgap36 has been linked to skin or hair coloration in any species. Experts are excited by this unexpected finding, which reveals a new molecular pathway and offers fresh insights into the complexity of feline genetics. As one researcher put it, "Everything you need to know about genetics you can learn from your cat."
