After a century of research, scientists have finally found what is responsible for the coat color of domestic orange cats.
Two teams from the US and Japan working independently from one another came to the same conclusion as to why orange cats are orange. It turns out that these notoriously crazy and rambunctious felines get their beautiful coat color from a genetic variation in the X chromosomes, confirming a 110-year-old hypothesis.
The research posted in bioRxiv, which has not been peer-reviewed for either team, provides substantial evidence that has been arrived at through different methods.
The gene behind orange cats
Scientists Greg Barsh from Stanford University and Hiroyuki Sasaki from Japan’s Kyushu University and their respective teams studied the genes of cats to determine what made those with orange coats different. In their studies, they found a particular protein on the X chromosome. The answer was hidden in the RNA of the feline and a deletion in their DNA.
“Our work provides an explanation for why orange cats are a genetic unicorn of sorts,” said Kelly McGowan, a Stanford University geneticist who participated in the US study and spoke to Tom Howarth of Newsweek.
In 1912, American geneticist Clarence Cook Little first theorized that the orange pigmentation was tied to the X chromosome. No one has been able to prove this until now, mainly because cats’ orange pigmentation is unusual in the domesticated animal kingdom in general. Most mammalian creatures get their orange marmalade coloration from mutations in a protein called Mc1r.
“It’s been a genetic mystery, a conundrum,” said Stanford University geneticist Greg Barsh to Sara Reardon at Science.
Little’s hypothesis predicted that whether males were orange or not was an all-or-nothing scenario, since they only have one X chromosome in their XY package. Meanwhile, females with their XX chromosomes could have orange with other colors such as tortoiseshells and calicos.
“Tortoiseshell and calico males do sometimes occur, but it’s usually due to an abnormality of the number of sex chromosomes, such as one too many X chromosomes (XXY), which also causes sterility,” said scientists from the University of Sydney and the University of Missouri in Columbia in an article about the findings published in The Conversation.
The protein on the X chromosome responsible for orange felines is known as Arhgap36. The reason why scientists never suspected this protein to be the one responsible for the variation in coloration is because it is involved in embryonic development. Barsh said they figured that, if this protein mutated too much, it would potentially kill the cat.
As it turns out, orange cats produce thirteen times the amount of RNA in comparison to non-orange cats. This means particular codes off DNA are needed to enable protein synthesis. The overproduction in RNA sends Arhgap36 into the cat’s fur proteins or melanocytes. When the researchers looked into the melanocytes, they indeed found an increased amount of the protein.