For decades, breeders have understood that the red (often called orange or flame) coat color in cats was X-linked. We knew male cats only needed one copy of the gene to appear red, while females needed two. But the exact mutation responsible in the genetics of orange cats remained elusive — until now.
In 2025, teams from Stanford University and Kyushu University independently identified the genetic cause: a deletion near the ARHGAP36 gene on the X chromosome. This breakthrough finally explains why red and cream cats appear the way they do and provides clarity that breeders can use in planning programs.
The ARHGAP36 Deletion
The deletion increases expression of ARHGAP36 in pigment-producing cells (melanocytes). This overexpression disrupts the usual production of eumelanin (black/brown pigment) and shifts the balance toward pheomelanin (red/yellow pigment). As a result, cats with this mutation display a vibrant reddish-orange coat rather than a black, brown, or chocolate-based coat (Science News).
This discovery is remarkable because when the genetics of orange cats was studied worldwide, all orange cats carried the same deletion, while non-orange cats did not. That means every red, cream, tortoiseshell, and calico cat shares the same underlying genetic change.
X-Linked Inheritance
Because the mutation is located on the X chromosome, inheritance patterns are predictable:
- Males (XY): Only need one copy of the orange allele, inherited from the mother, to be red. This is why male orange cats are more common.
- Females (XX): Need two copies of the orange allele (one from each parent) to be fully red or cream. With only one copy, X-inactivation leads to a patchwork of orange and non-orange expression — producing tortoiseshell or calico coats.
This explains why female red Ragdolls are so rare. Unless a breeder has a female carrying orange (O) bred to a male carrying orange (O), fully red daughters are unlikely. Most catteries only produce red males and tortie females.
Cream: The Dilute Version of Red
The dilution gene (d/d) modifies pigment intensity across all colors. When paired with the orange allele, it produces cream — a softer, buttery orange tone. Cream cats are genetically red, just with dilution applied. This is why breeders often refer to “red/cream lines” together: they are different expressions of the same orange mutation.
Breeding Implications for Ragdolls
For Ragdoll breeders, this discovery reinforces what many already track in pairing plans:
- Producing red females: Requires a dam carrying orange (O) and a sire carrying orange (O). At Rarity Ragdolls, we can achieve this through our cream bicolor female Isabella, which allows us to produce true red daughters — something many programs cannot do.
- Cream kittens: Occur when the dilution gene is present alongside orange. Our male Kurt is a cream van, an excellent example of this genetics at work.
- Tortie and calico daughters: If only one parent contributes the orange allele, female offspring often express it in patches along with their other base color (seal, blue, chocolate, etc.). Our Autumn (seal tortie) and Ginger (blue-cream tortie) show this beautifully.
- Orange boys: With the right pairings, males like our Nian Gao (red bicolor) inherit the orange allele and express it fully.
Tabby Influence
All red cats carry tabby striping to some degree, whether they are officially registered as tabby/lynx or not. The orange pigment makes tabby expression more visible, especially on the face, legs, and tail. Breeders should expect even “solid” red points to show faint striping.
Why This Matters to Breeders
This discovery is more than an academic milestone. For breeders, it confirms that in the genetics of orange cats:
- All red/cream cats, regardless of breed, share the same ARHGAP36 deletion.
- Producing red females requires intentional planning and the right parents.
- Dilution and tabby interact with orange in predictable ways, allowing breeders to project possible kitten outcomes with more confidence.
In practical terms, this means that red and cream Ragdolls — long admired for their rarity — can now be understood at the molecular level. This knowledge adds weight to breeder education and transparency, especially when explaining to kitten buyers why red females are special or why creams appear alongside reds in certain litters.
References
- Stanford Medicine (2025) – Scientists identify the mutation behind orange cats
- Current Biology – Molecular and genetic characterization of sex-linked orange coat color in the domestic cat
- Science News – A single gene mutation explains why some cats are orange