According to the World Animal foundation, there are 373 million domestic cats in the world, and 80 percent of the orange kitty population are male. For years scientists have know that orange in a cat’s coat was related to the X chromosome, but didn’t know why. But a team of researchers from Kyushu University say it all boils down to a tiny piece of missing DNA.

The research found that a tiny deletion of 5100 DNA letters, of which there are typically 2.5-2.8 billion, are missing. In a vast sea of DNA letters, the missing is only 0.0002% but even this can make a massive difference and it is only found in orange, tortoiseshell and calico cats.

This happens because the genetic change impacts pigmentation production. It depresses eumelanin, the genes that would typically make black or brown fur and amps up the pheomelanin that makes orange pigment.

Because female cats have two X chromosomes, one from each parent, and the gene sits on the X chromosome, only one X is active in each cell. This leads to a medley of colors they inherit both orange and non-orange genes — and ultimately calicos and tortoiseshell cats are almost always female.

If a male cat inherits the orange version of the gene, he’ll be all orange. But for a female to be fully orange she has to get that orange gene from both parents — which is much less likely. That’s why 80 percent of all orange cats are male.

This new research adds the ARHGAP36 to the list of genes that impact animal color and solves a long-standing feline mystery.

The study was published in Current Biology.

More like this: Bonobos adjust their communication based on ignorance