Leopards, cheetahs, Egyptian rats — many kinds of cats have surprising spots. Other cats, such as tigers, have stripes; other cats, such as lions, have no patterns on their hair. But how do cats get their spots? Scientists don’t have a full answer to this question, but they have found several clues. “We don’t know why some cats have spots and why some cats have stripes,” Dr. Gregg Barsh, emeritus professor of genetics and pediatrics at Stanford University, told Live Science.
But researchers have identified two genes that influence the size and shape of spots — as well as stripes — in both domestic cats and wild cats. Domestic cats with one or two normal copies of a gene called TacPep have stripes, Barsh and his colleagues reported in a 2012 paper published in the journal Science.
But according to the same paper, as Live Science previously reported, cats with mutations in both copies of this gene (one from their mother and one from their father) have spotted or curled hair. These TacPep mutations lead to the classic tabby cat pattern, Leslie Lyons, a cat geneticist at the University of Missouri College of Veterinary Medicine, told Live Science.
TacPep mutations can also alter spots — at least in cheetahs. Cheetahs are known for having black spots on a yellow-brown background. But the “king cheetah” — which has mutations in both copies of the TacPep gene, according to a 2012 Science paper — has large, blotchy spots. Along the spine, the spots align themselves into stripes.
Although spotted domestic cats are not obviously striped, they do appear to have a normal version of Takpep, according to Eduardo Eizirik, a professor of genetics at the Pontifical Catholic University of Rio Grande do Sul in Porto Alegre, Brazil. As part of a study published in 2010 in the journal Genetics, he mated a spotted domestic cat with a non-spotted cat.
Eizirik and his colleagues concluded that the spotted cat they started with — an Egyptian Mau — must have the normal Takpep gene, because some of its descendants had stripes. The team also speculated that one or more other genes in the spotted cat had the effect of breaking up the stripes normally formed by Takpep and turning them into spots. It’s still unclear what those other genes are, he said.
Another gene that affects spots, according to Barsh, is Dkk4. The Abyssinian breed of domestic cat has one or two mutated copies of the Dkk4 gene. At a glance, its coat appears to be a solid brown or cinnamon color. However, another way to look at it is that it is a coat dotted with small black spots, Barsh said.
Servals are wild cats with large spots, and they have two normal copies of Dkk4. So, if you cross an Abyssinian cat with a Serval, as has been done, some of the offspring inherit one normal copy of Dkk4 and one mutant copy, Barsh explained. These offspring have spots that are larger and sparser than the speckled spots present on the Abyssinian parent, but smaller and more numerous than those on the Serval parent.
Although mutations in Taqpep and Dkk4 can modify spots and stripes, these genes themselves do not control whether the cats have spots or stripes. Tigers with normal Takpep genes have stripes, while cheetahs with normal Takpep genes have spots, Barsh said. While mutations in Takpep can make a cheetah’s spots turn into spots, the spots don’t turn into stripes.
And as Eizirik’s work has shown, domestic cats with normal Takpep genes can be either striped or spotted. “There has to be something else, a third gene, that’s helping to create those spots,” Lyons said.
