Why Does My Cat Look Like That? Adventures in Cat Genetics!

cat facts

Impress your friends with these cat facts based on genetics research.

I come from a whole family of cat people. A month after moving into my first solo apartment, I walked into my local Humane Society and scooped up an orange-and-white kitten, a male, out of a pile of otherwise all female kittens who looked just like him. When I told people the story, more than one responded with “I thought all orange cats were boys!” I was soon fielding questions about Jonah’s (yeah, that’s my cat’s name) family of origin. I thought I was pretty knowledgeable of cat facts, but there was an area of feline culture where I was severely lacking: genetics.

A little digging plunged me into a fascinating world of cat genetics. It turns out that cats, especially their coat colors, have been used as an example to teach genetics for years. And because cats are domesticated animals that were intentionally bred, breeders had quite a bit of knowledge about how individual traits were passed on long before scientists got involved. Learning about why cats look the way they do can be a fun way to try to wrap your head around the mystery of genetics, even if you don’t consider yourself a science person.

The way cats look is primarily controlled by their genes. They get half of each gene (or one allele) from each parent.

What color is your cat? Genetically speaking, the answer might not be what you think! It’s sometimes said that cats have only two colors: black and orange. (Cat breeders often refer to orange cats as red — but they also call a kitten’s parents the “dam” and the “sire,” so I’m sticking with orange.)

You’re probably thinking, “There aren’t only two colors,” and you’re correct. What’s actually going on is that there are two different genes controlling the pigment in the fur. Those pigments are made of melanin. There’s eumelanin (black) and phaeomelanin (orange).

The black gene has three alleles, usually represented as B, b, and b’, and they create the colors black, chocolate, and cinnamon, respectively. Cinnamon and chocolate are pretty rare colors in the cat world, and because B is dominant, BB, Bb, and Bb’ all produce black cats. By black I don’t mean all-black, I just mean a cat that has some true black fur. A tabby cat on which the darkest color is black is, at least in terms of genes, a black cat. If you have a gray cat, your cat is black (so BB or Bb or Bb’), but the black pigment is being affected by another gene, to create “dilute black.” Dilution is recessive, so dd turns your black cat gray, but DD and Dd leave the dense coloring the way it is.

cat facts

Both of these cats are black, according to science! Via iStock

The orange gene works similarly, except for a couple of key differences. The first is that orange kind of writes over black, so if a cat gets the dominant orange allele O, you’ve got an orange cat now…probably.

The deciding factor is the location of the orange gene: it’s on the X chromosome. Why does that matter? Well, as with other mammals, female cats have two X chromosomes (XX) while male cats have an X and a Y (XY). When a gene is attached to the X chromosome, it gets passed on differently depending on the sex of the kitten. A male kitten gets his X chromosome from his mother, and along with it either a dominant O (making him orange) or a recessive o (leaving him black). But a female kitten gets an X chromosome from both sides of the family. An OO combo makes her an orange cat (there are about half as many female orange cats as male ones) and an oo leaves her black. But something strange happens with an Oo combination. Rather than going with the dominant trait and being all orange, she’s only sort of orange. Random patches of black show through, which gives you what’s referred to as tortoiseshell, of if there’s white involved (we’ll get to white later), calico.

cat facts

iStock

If you’ve heard that all calicos are girls, this is why. You need two X chromosomes to make a calico. Now, intersex cats do exist, and while it isn’t common, there are cats born with three sex chromosomes (XXY). Thoparse cats typically look male but may be calico or tortie.

Remember the dilute gene mentioned above? It works the same on orange (and calico and tortie). Orange becomes cream; black still becomes gray.

Now, let’s talk about white markings, also knowing as white “blocking.” Most white blocking is caused by the same gene that literally blocks pigment from being expressed on certain parts of the body. SS gives you a cat with white, as does Ss, and ss creates a cat with no white. So if your cat has some white on its body but isn’t all white, you’re looking at the blocking gene. What’s harder to understand is why some cats have more white than others. There are some people who believe that an SS combination will produce a mostly white cat (because it creates more blocking) whereas Ss produces cats who are approximately half white. Others think the blocking gene itself only controls whether or not blocking is present, and the degree is controlled by other genes.

Though we know a lot about cat genes, we don’t know it all, and there are still debates. What we do know is that color blocking seems to start around the paws and then move up the body.

Cats that are all white have a totally different gene at work, as do albino cats.

cat facts

Each of these Maine coon kittens is unique, but they all have white blocking. Via iStock

What if your cat is a tabby? First, to be clear: Every cat you’ve ever seen is a tabby. Technically, genetically, all cats carry a tabby gene, which we’ll get to in a minute.

Whether or not your cat looks like a tabby is controlled by something called the agouti gene. That’s just a fun way to say striped, or banded. Only we’re not talking about the stripes on the entire cat; we’re referring to stripes on individual hairs. If you’ve ever been around a shedding tabby (in other words, if your house is often covered in a layer of fur), you’ve probably seen these hairs that are more than one color. Those are called agouti hairs. They’re pretty cool-looking! These fill in the spaces between the solid-colored stripes on your tabby cat.

cat facts

The variety of color is created by individually banded hairs. Via iStock

So if your cat has the dominant version of the agouti gene, AA or Aa, it will have these cool striped hairs, and because they look different than the solid color hairs, you can easily see whatever tabby pattern your cat has inherited. But if your cat has the recessive aa, it won’t have any agouti hairs. The tabby pattern is still technically there, but it’s impossible to see. The stripes are exactly the same as the background, so they’re indistinguishable. When my pure black cat was a kitten, in certain lights you could see the faintest hint of a stripe here and there, which I’m told isn’t uncommon.

There’s one important exception here: orange cats. Something about the way the orange pigment is dispersed means it doesn’t care what the agouti gene is doing; there’s going to be some agouti hair no matter what. That means all orange-and-cream-colored cats have a tabby pattern, to some degree (some breeders work hard to create something close to a “solid” orange-colored cat), and it’s much harder to tell at a glance whether they carry the dominant agouti gene.

The tabby pattern itself is controlled by yet another gene — or, according to a 2010 finding, maybe three separate genes interacting with each other. Cat breeders still tend to describe it as one gene, with three different alleles, probably because that’s what they did in the past and it still helps predict breeding results. There are three main tabby patterns: mackerel tabby (the most common, tiger stripes), ticked tabby (almost no stripes except on the face and legs, but lots of agouti fur on the body), and classic tabby (also called “blotched” — instead of stripes, they have big swirly markings on their sides).

cat facts

This Scottish fold kitten shows the classic tabby pattern. Via iStock

All of these cat facts are really the tip of the iceberg, and there are plenty of genes we haven’t even touched on. It’s a lot of information, and some of it comes with conflicting opinions. Consider this a good start in cat genetics. You can find lots more information, including facts about pointed cats (such as Siamese), smoke patterns, the connection between white fur and deafness (yes, really), and the length of fur. In general, it’s LL or Ll for short-haired cats, and the recessive ll creates long hair (but of course other variables are controlled by other genes).

If you’re like me, you’re trying to see if you can determine what’s going on with your own cat’s genes by what you see. Well, you kind of can! You can use this handy gene map from a personal blog called Three Yard Cat (which also has a wealth of information on cat genes). You might not know what’s going on with every gene, but it’s kind of cool to see what you do know — and you’ll be able to understand even more if you’ve seen your cat’s parents. A few sites also have cat gene calculators, which show what a cat couple’s kittens would likely look like.

Although a lot of cat facts come from humans’ history of breeding cats, I’m not advocating backyard breeding for conducting genetics experiments.  Research suggests that cats who are spayed or neutered live longer, happier lives. end

 

Next Article