Scientists solve 100-year-old mystery behind why most orange cats are boys

In a groundbreaking discovery that unravels a century-old mystery about cats, scientists have identified the peculiar genetic switch that gives felines their vibrant orange colour, explaining why most ginger cats are male. This revelation uncovers a mechanism unlike anything observed in other mammals.

A group led by Stanford Medicine geneticist Chris Kaelin has traced the origin of ginger coats to a minuscule deletion on the X chromosome. This causes an unexpected gene, named Arhgap36, to activate in pigment-producing cells.

This malfunction blocks a late step in the melanin pathway, directing fur away from dark hues and towards bright orange. Speaking to ZME Science, Chris said: "For more than a century, orange coat colour in cats has been recognised as an exception to the usual rules."

READ MORE: Gold dust found in the needles of Christmas trees

READ MORE: Bones of young woman 'abandoned' at South Pole could rewrite history of Antarctic exploration

The recent study pinpoints the anomaly: not a faulty pigment gene, but a gene activating where it typically wouldn't - "a very unusual mechanism" of misexpression in a specific cell type, reports the Daily Star.

So, why are most orange cats male?

The orange trait is located on the X chromosome. Males (XY) require just one copy to become ginger, which is why approximately 80% of orange cats are males.

Females (XX), on the other hand, need two copies to be entirely orange; otherwise, random X inactivation results in the classic tortoiseshell or calico mosaic of orange and black.

In contrast to most other mammals with yellow or orange shades, the effect in cats comes from mutations in one of two pigment genes that are not sex-linked - making domestic cats a remarkable exception.

How they discovered it.

The research team examined DNA from ginger and non-ginger cats, collecting specimens from spay and neuter clinics whilst utilising cutting-edge genomic technology that wasn't accessible ten years ago.

Their investigation pinpointed a tiny deletion close to Arhgap36 on the X chromosome. This alteration essentially switches Arhgap36 "on" in pigment cells, disrupting the final phases of dark pigment creation and exposing orange.

Aliens are using AI to hide from us, and the mother of all waves spotted in the Pacific - all this and more in our latest weird science newsletter

Arhgap36 has never previously been connected to coat colour in any species. In humans, it's associated with particular developmental signalling functions and certain neuroendocrine tumours - highlighting just how surprising its appearance in cat colouring truly is.

No, ginger cats aren't genetically destined to be cheeky.

Pet owners insist orange cats possess larger-than-life characters, yet the scientists discovered no variations in Arhgap36 activity beyond the skin.

Analysis of tissues including brain, heart, kidney and adrenal gland revealed no expression alterations between orange and non-orange cats.

This indicates the mutation's impact is extremely confined to pigment cells. Behavioural folklore, meet scientific fact: since the orange gene is X-linked, you encounter more orange males - and humans typically create narratives about what they observe most frequently.

An old gene with a very modern twist The mutation isn't a recent phenomenon. Medieval illustrations dating back to the 12th century depict calico cats, suggesting that the orange-linked genetics have been present since the early days of domestication.

What's novel is the understanding: rather than the typical "break the pigment gene" approach, the cat genome took an unexpected turn, utilising a regulatory hiccup to repurpose a gene in the wrong place at the right time - a striking demonstration of evolution's talent for improvisation.