Hi everybody, Kissy here! I’m really excited because this week I get to have the whole column all to myself! As you can see from my photo, I’m an orange tabby cat (which Mama sometimes calls a “marmalade cat”) … and a quite beautiful one at that, I might add.
When Mama adopted me and showed my pictures to the world, lots of people remarked on how rare orange female cats are. Mama says she’s seen quite a few orange girl cats, so together, we set out for some answers. We interviewed Dee Walter Kruleski, a professor of biology at HACC, Central Pennsylvania’s Community College, who told us the facts about female orange cats and lots of other cool facts about cat fur color inheritance. So, without further ado, let’s get on with it.
Kissy: I’ve heard that female orange cats are very rare. Why is this?
Dee: Well, it’s not that orange female cats are rare, it is simply that an orange cat is more likely to be a male. For a female cat to be orange, she must inherit two orange genes — one from her mother (orange, calico, or tortoiseshell) and one from her father (who must be orange). A male cat needs only one orange gene, which he gets from his mother (orange, calico, or tortoiseshell). This is because the gene that codes for orange fur is on the X chromosome, and like humans, females have two Xs and males are XY. Genes on the X chromosome are said to be sex-linked.
Kissy: Wow, so that means my father for sure was an orange cat. How cool is that? Is the same thing true for orange tabby (marmalade) cats? Mama says she’s seen a lot of female orange tabbies.
Dee: Yes, although the striping pattern is coded for by a completely different gene.
Kissy: Why is it super-rare to see a male calico cat?
Dee: Because in order for a male to be a calico, he must have the feline equivalent of Kleinfelter Syndrome and he is an XXY male. Because a calico male has an extra X chromosome, he is most likely sterile (cannot father kittens).
Kissy: Can you explain a little bit about how fur color inheritance works in calico/tortoiseshell and orange cats?
Dee: Well, orange fur is due to what is known as dominant epistasis. It actually changes black pigment into orange! This is an example of gene interaction — where one gene changes the expression of another.
Calico or tortoiseshell coloration is the result of something called X-inactivation (also known as dosage compensation). Female mammals (including humans) have one X in every cell inactivated (shut down) as an embryo. In approximately half the cells, the paternal X (one from the father) is expressed, and the other half of the cells the maternal X is expressed. So when you look at a calico cat, where you see black fur –that came from one parent and where you see orange fur, that came from the other parent. Thus all female mammals are genetic mosaics!
Kissy: Wow, that’s amazing. And complicated! How many genes are involved in determining a cat’s fur color?
Dee: Many! Here are a few of them:
- Agouti vs. non-agouti: Provides the lighter fur background with striped cats.
- Black vs. non-black
- Color deposition: Determines how pigment is deposited, and also affects eye color.
- Dilute vs. non-dilute: Gray is a diluted form of black and tan/beige is a diluted form of orange.
- Spotting: If two dominant genes are inherited, a cat will have white on more than 50% of their body. If a cat has one dominant and one recessive gene, then the cat will have white fur on less than 50% of their body. If she gets two recessive genes, there will be no white on the body!
- White vs. non-white: Just one white gene and the whole cat will be white! It is called a masking gene. A white cat could have the genetics to be a calico, black or any color cat but the white gene hides the other genes’ expression and the cat appears all white. White cats are not albinos unless they have red eyes. Albino cats are extremely rare and albinism is the result of color deposition and not the white gene.
- There are also genes for tabby stripping, silver tipping and seal-pointing.
Kissy: Wow, that’s cool. I must have one dominant and one recessive spotting gene because I’ve got a little white spot on the end of my tail, and that’s all the white fur I’ve got. Anyway, Mama says some purebred cats are more likely to inherit certain illnesses. Are there any kinds of inherited illnesses or problems that tend to occur more in orange or calico/tortie cats than in the general cat population?
Dee: Not to my knowledge.
Kissy: Are there other sex-linked inheritance traits in cats (other than the obvious plumbing and hormone stuff)?
Dee: Many! Believe it or not, most genes on the X chromosome have nothing to do with sex but how the cells in the body work. Fortunately, there are few sex-linked genetic disorders known to occur cats.
Kissy: Any other cool stuff you want to tell me about orange cats, calico cats and sex-linked inheritance?
Dee: I think it really cool that cat coat color is used in virtually every biology and genetics textbook to illustrate X-inactivation and sex linkage. My students must solve genetics problems, and predicting the appearance of kittens is fun!
Kissy: One last thing: Mama says you run a cat sanctuary. Would you like to say more about that?
Dee: Shawnee Om Shanti Sanctuary is a living memorial to my daughter and only child, Shawnee, who died unexpectedly in 2001. It started with me feeding feral and dumped cats in the woods where I used to live. I gradually had shelters built for them, trapped and had them spayed/neutered and vaccinated. Last year I was forced to move, so we built the cats a swell two-story house, complete with a play yard and fenced to keep them safe. We are continuing to work on it — the “Cat House” has electricity, is insulated and has heat and fans. Soon we will be adding a big porch to the cat house! I hope to post videos of the sanctuary on YouTube in the near future. We are located in South-central Pennsylvania.