Stanford scientists solve one of the world's great cat mysteries

Caramel, a 6-month-old cat, waits with his owner backstage before competing in an orange cat competition on July 2, 2023, in Bangkok, Thailand. Lauren DeCicca/Getty Images

What do Garfield, Heathcliff and Puss in Boots have in common? They’re all cats, they’re all orange and they’re all males. This is no accident. As it turns out, most orange cats are male, while almost all calicos and tortoiseshells are female. This difference in hair color has puzzled scientists and cat lovers for decades, until now.

Science Magazine wrote that a team led by Stanford geneticist Greg Barsh has uncovered the genetic mutation responsible for orange fur. Orange coloring comes from a gene called Arhgap36, found on the X chromosome. Since males only have one X chromosome, they express this mutation fully, leading to their signature fully orange coats. Female cats, with two X chromosomes, end up displaying a mix of colors, creating calicos and torties.

To identify the mutation, Barsh’s team analyzed skin samples from spay-neuter clinics. They found that melanocytes — pigment-producing cells — from orange cats produced 13 times more RNA from the Arhgap36 gene than those from non-orange cats.

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The researchers confirmed their findings by analyzing a database of 188 cat genomes, and a separate study by scientists in Japan reached the same conclusion.