Cat lovers will tell you that you can tell a lot about our feline friends just from the color of their coat. Tortoiseshell cats have an array of personality traits – they are known for being curious, clever, happy and compassionate. White cats tends to be calm, playful, affectionate. In Japan, black cats are considered to be a sign a good luck. Ginger tabbies meanwhile have a reputation for being friendly and easy-going, although be careful as some have a temper to match.

There is also a theory that cats, like dogs, take after their owners, adopting many of the same characteristics.

There is no scientific basis for any of these beliefs and cats remain as much a mystery to humans today as they have for thousands of years.

There are between 42 and 100 different cat breeds in the world today – of which, 40 to 71 are classified as “domesticated” breeds. In the United States, 95% of house cats are classified as domestic long hair or short hair breeds.

Of the total global feline population, about a fifth are ginger tabbies – flame-haired moggies – just like Garfield, Nekobus from My Neighbor Totoro, or Puss in Boots from Shrek. For decades, researchers have pondered how different breeds of cats have the ability to give birth to ginger offspring, and this month, science finally managed to crack one of the biggest mysteries in feline genetics.

Why are most ginger cats male?

Two independent teams of scientists from Stanford University in the United States and Kyushu University in Japan —have identified a unique mutation found exclusively in domestic cats. The paper A deletion at the X-linked ARHGAP36 gene locus is associated with the orange coloration of tortoiseshell and calico cats details why some cats have a ginger or orange coat.

This new breakthrough finally offers a definitive explanation for the enigma of orange fur, shedding light on a genetic trait never before observed in other mammals.

The report states that the X-linked orange (O) locus in domestic cats controls an unknown molecular mechanism that causes the suppression of black-brownish pigmentation in favor of orange coloration. A 5.1-kilobase (kb) deletion within an intron of the X-linked ARHGAP36 gene, encoding a Rho GTPase-activating protein, is closely and exclusively associated with orange coloration. The 5.1-kb deletion seems widespread in domestic cats with orange coat coloration, suggesting a single origin of this coat color phenotype.

So why are over 80 percent of ginger cats male? Males have only one X chromosome, a single copy of the ARHGAP36 orange gene is enough for their entire coat to express the color. In contrast, females, who possess two X chromosomes, are only fully orange if both carry the gene. If only one does, the result is a calico or tortoiseshell pattern, where orange patches alternate with black or brown.

First time gene is linked to pigmentation

This finding is remarkable for a number of reasons. Firstly, ARHGAP36 had never been linked to pigmentation in any mammal before. And secondly, the mutation doesn’t occur within the gene itself but in an adjacent fragment, suggesting an extremely fine-tuned and specialized activation mechanism.

“These ginger and black patches form because, early in development, one X chromosome in each cell is randomly switched off,” Professor Hiroyuki Sasaki who led the Japanese study explained. “As cells divide, this creates areas with different active coat color genes, resulting in distinct patches. The effect is so visual that it has become the textbook example of X-chromosome inactivation, even though the responsible gene was unknown. Identifying the gene has been a longtime dream, so it’s a joy to have finally cracked it!”

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