Why do some cat siblings look so different?
If you’ve ever seen a litter of kittens, you may know that many of them barely seem related. With coats ranging from black to white, tortoiseshell to tabby, and even long to short hair, littermates can be very different from one another.
So why do kittens often look nothing like their relatives, even though most human siblings look similar? The answer lies in the complex nature of the cat’s coat. genetic and a phenomenon of ovulation in cats.
The Genetics of Cat Coat Color
The Cat Fanciers’ Association recognizes dozens of coat colors and patterns, ranging from basic solid colors to more distinctive patterns, like the rosette tabby coat of the Bengal or the checked coat of the Abyssinian. All these variations come from a complex system of interacting genes.
“There are a number of different genes involved in cat color and pattern, and it’s particularly complicated because some genes overwrite other genes,” Jonathan Lososprofessor of biology at Washington University in St. Louis and author of “The cat’s meow: how cats evolved from the savannah to your couch” (Viking, 2023), told Live Science.
Control of different genes solid coat colors, spots, patterns and hair length. According to Losos, these genes come in a “hierarchy” – for example, a genetic mutation for white fur, called dominant white, will override all other colors. Other genes control patterns such as tabby fur, and these work in combination with color genes to produce a coat. Some cat coat colors are also sex-linked, meaning the gene is contained on the X chromosome, so the range of colors and patterns for male and female cats is different. Typically, only female cats have calico or tortoiseshell patterns.
If all these genetic variations are difficult to track, that’s the problem. Even a few different combinations of a handful of genes can have drastically different results in terms of coat color, pattern, and length, and this is one of the main reasons why cat littermates can look so different even when they have most of the same genes. But there is another factor that makes cat litter genetics even more complicated.
Multiple authorship
Female cats are induced ovulators, meaning their reproductive systems do not release eggs until they have already mated with a male. This increases the chances of successful fertilization, but it also has a disadvantage: the female can release several eggs during this period, so if she mates with another cat in the coming days, she may become pregnant with several males.
This means that kittens from the same litter can have more than one father, so some siblings are only 25% genetically related, leaving much more room for variation in their appearance. This phenomenon is called heteropaternal superfertilization, and it’s actually not that rare in the animal kingdom; dogs, sheep And cows can also have multiple births with more than one father. In extremely rare casesheteropaternal superfertilization has even been documented in humans.
“I don’t think it’s unusual for cats to do this,” Losos said.
Scientists aren’t sure why heteropaternal superfertilization is so common in cats, but there are theories.
On the one hand, induced ovulation might be a more ingenious way to go about mating, and heteropaternal superfertilization is a side effect of induced ovulation. “Maybe it’s a evolutionary adaptation that allows the mating process to be more efficient,” Bruce Kornreichdirector of the Cornell Feline Health Center, told Live Science. He explained that releasing eggs only after mating prevents eggs from being “wasted”, so the female cat’s reproductive system does not use energy to produce unnecessary eggs.
Multiple paternity within a litter might even have its own benefits, Losos noted. When littermates have different fathers, it increases the genetic diversity of cat families, which is generally good for survival.
Heteropaternal superfertilization is much more likely to occur in urban areas, where the concentration of cats is high and tom territories are likely to overlap. In fact, a 1999 study found that 70–83% of urban cat litters had more than one father, while only 0–22% of rural litters had more than one father, making diverse litters the norm rather than the exception.
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