You know why virtually all tortoiseshell cats are female, right? It’s all due to genetics. Well, maybe some of you don’t, so a quick explanation is in order to introduce today’s felids.
Tortoiseshell cats, or “torties,” are cats with patches of orange and black fur, and sometimes a bit of white. Here’s one:
How do they differ from calico cats? Only because calicos have more white in their fur. But, like torties, calicos are almost always female. Here’s a calico:
Why are these cats nearly always female? It’s because, as in humans, female cats have two similar sex chromosomes (XX), while males are XY, with the Y chromosome largely genetically inert (it does carry sex-determining genes). It turns out that the X chromosome (but not the depauperate Y) carries a gene that affects fur color, and that gene has two forms, a “black” form and an “orange” form.
The other thing you need to know is that, during development of females, one X chromosome is completely inactivated in each cell. That has evolved to keep the “dosage” of gene products identical between the sexes. So an XY male produces product from one X chromosome, and so do XX females, because one X is switched off in each cell (this mechanism is called “dosage compensation”).
The inactivation occurs at different stages of development, and is random, so, for example, early in development one cat embryo cell will have one of its X’s inactivated, and all the descendants of that cell will have the same X inactivated. But since inactivation doesn’t occur at the very beginning, a live female cat will be a mosaic, with one of the X’s inactivated in part of its body and the other X in other parts. Which X is inactivated seems to be random.
So imagine a female cat with two X chromosomes, one carrying the gene coding for black fur, and the other for orange. If the black-gene-carrying X is inactivated, those epidermal cells will express only the orange gene, producing orange fur. If the “orange” X is inactivated, the cat makes black fur. If a female carries both forms of the gene (i.e. she’s a “heterozygote” for black-X and red-X), the random inactivation of X’s will lead to a cat having patches of red and black fur, i.e., a tortie. Males, having only one X, cannot be mosaics, and so will be either all black or all red. That is why male calicos and torties are almost nonexistent.
What about the calicos? Well, to be a calico you still have to have red and black patches, ergo you have to be female, but some of these cats have an additional gene, called “piebald”, which is not on the sex chromosomes. That gene has a form, S, causing white spotting (Hili has it), and is dominant over the alternative form “s”, so if you have two copies of the piebald form (S/S) you get white patches, if one copy (S/s) copies you have smaller white patches, and if you have no copies (s/s) you don’t have any white. The only difference between calicos and torties, then, is that calicos have at least one S form of the gene as well as being heterozygous for the X-linked black and red genes. Male cats, of course, can also show piebaldness, since the gene is not on a sex chromosome.
If you want this all explained with diagrams, go here, or go here for a longer explanation.
That is a long-winded but necessary introduction to a true rarity, a male tortoiseshell cat named Harry who has shown up at a cat shelter in Bonnyrigg, Scotland; his owners were allergic to his fur. Here’s the cutie, just a 3-month-old kitten:
Harry with Nicola Zelent from Lothian Cat rescue, photos from the Daily Record (link above):
How can you have a male tortoiseshell cat? It has to have two X chromosomes to get that fur pattern. But it also needs a Y chromosome to be a male. And, indeed, the rare male torties have the chromosome constitution XXY, and are heterozygous for the X-linked fur-color genes. But because their sex chromosome balance is messed up, these male cats are sterile; they are, in effect, “intersexes,” but I suspect are identified as males because they have male-like genitals. To quote from the article:
Margaret Riddell [the vet] said: “When I heard the cat was called Harry, I said to the owners, ‘I think that might have to be a Harriet’.
“I had to change my words when I discovered it was male. I’ve never seen one before and I’ve been a vet for more than 30 years.”
Well, it’s not really a “male” in the conventional sense; it’s an intersex. But no matter, it’s rare, it’s cute, and the good news is that it doesn’t have to be neutered.
The XXY condition occurs in humans, too, though rarely (in roughly 1 in 1000 individuals identified as male). It produces what’s called Klinefelter Syndrome. Because of the unbalanced sex chromosomes, that condition, as in cats, produces sterile males as well as a variety of traits described by the NIH:
Affected individuals typically have small testes that do not produce as much testosterone as usual. Testosterone is the hormone that directs male sexual development before birth and during puberty. A shortage of testosterone can lead to delayed or incomplete puberty, breast enlargement (gynecomastia), reduced facial and body hair, and an inability to have biological children (infertility). Some affected individuals also have genital differences including undescended testes (cryptorchidism), the opening of the urethra on the underside of the penis (hypospadias), or an unusually small penis (micropenis).
I suspect that an inspection of Harry’s willy (note the two royal names) would show abnormal but male-looking genitals.
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Okay, enough biology for the morning. Here’s a cat with paper-related OCD in a video that’s garnered 1.8 million views in the last nine days. Who knows what it’s up to?
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College Humor has a series of gifs showing cats giving high fives. Here are a few:
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Finally, as lagniappe, at the latest Oatmeal the cats get their back:
In the first gif, that’s not a “high five”. That’s a “terrorist fist jab“. 😉
I like the third one where the cat thinks about whether a high five is in order, then gives one half-heartedly.
Only the last one counts as a proper high five.
Harry looks like a really cute cat! I love the royal, “Harry’s willy” too.
I think OCD cat enjoys the sound of the paper & perhaps how it feels on his/her paws. He/she seems almost hypnotized by it.
Yes, I think it feels good, and is fun…but, it also looks like he/she is doing a bit of “nesting” motion before settling down on that lovely crinkly paper
Surprised nobody else has yet observed that Harry’s willy is hairy….
b&
Jerry… and you were worried about lack of interest in science posts? That was both fascinating and felid ….
Further thought….
It might be sterile but would it show any male behavioural characteristics? Such as spraying?
I agree! For once, I totally understood and appreciated learning the mechanics of it.
I liked the genetics info. Keep it up, this old physics teacher is learning new science.
That is really cool about the male tortoiseshell. I knew they were out there somewhere.
I used to teach genetics, and for fun I would go over the genetics of our domesticated animals and plants. I did not know, however, that the piebald allele had different degrees of spotting in the homozygotes and heterozygotes. So I learned something, even before my morning coffee.
As a cat lover and biologist I just couldn’t resist buying and reading a book I came across while browsing a bookshop some years ago. It’s called “Cats are not peas: A calico history of genetics”. It is a very enjoyable book writen by a non-scientist, explaining the history of genetics for the general public. The author, Laura Gould, was drawn to genetics and to writing this book when she acquired George, a calico kitten that turned out to be an XXY male. It is a very enjoyable book and a quick look at the Amazon website shows there even is a 2nd edition that came out in 2008.
I read that book! “High five!”
The tortoiseshell colours of black and red can be modified by other genes such as the recessive dilute gene (dd) which softens the colours, turning black to gray or blue, and the red to cream. So you can have a dilute tortoiseshell or blue/cream cat, or a dilute calico cat. We have a beautiful semi-longhaired blue/cream female named Azul. The colouring extends to her paw pads, some of which are a pale cream colour and others which are a gray-blue colour.
Very interesting genetics, especially since one of our cats is a Torti – and a female. Had no idea of this but apparently the cat expert (wife) did.
I wonder if the reasons for the male are similar to the donkey?
Obviously, the cat in the video is thinking about dog-earring the page, but can’t bring it self to do it. 😉
The paper cat is performing its solemn duty of preventing its owner from looking at paper. As everyone knows, the act of its human looking at paper is not allowed. A cat must lie down on the paper and get all cute and purry. Paying bills? Doing homework? Nope. You will pet me. Now.
Well of course.
My female cat has both tabby markings and tortoiseshell colorings. Apparently, this combination doesn’t deserve a cool name like “torbie”. I’ve seen lots of cats with this combination of markings at the animal shelter (while shopping for the current cat). Is there a name for this?
As for the paper OCD cat, I see the same expression on my cat when she does her morning “kneading”. I’ve also had cats that will repeatedly lift something and let it fall. Then I’d wake up.
Actually the cool name Torbie is correct according to Wikipedia: “Occasionally tabby patterns of black and brown (eumelanistic) and red (phaeomelanistic) colors are also seen. These patched tabbies are often called tortie-tabby, torbie or, with large white areas, caliby. Tortoiseshell can also be expressed in the point pattern.”
The point pattern is the classic Siamese pattern, where the colour is restricted to the face, ears, tail and legs of the cat. In a tortie point cat those areas are a mix of the black and red tortoiseshell colours, or blue and cream if it is a dilute tortie point. And to make things even more complicated, you can have a torbie point cat where the black and red point colours have the tabby striping. Then there is the lynx point pattern where the standard tabby markings are restricted to the points of the cat and can come in the various tabby colours. Cat breeders have quite a genetic palette to work with.
Now I want that kitten just cause of its genetics.
Here is an amazing video that talks about the “stripey”-ness of females: http://www.youtube.com/watch?v=BD6h-wDj7bw
The most amazing thing to me is that human females would be stripey too, if we had cool colors like cats.
Also, I want a tortie now.
So basically all female mammals are mosaics as far as their X goes.
Something we knew, of course, but did not really think about (at least I did not really). The torties are just drawing our attention to how awesome they, and we, are.
What causes the striped pattern in tabbies, tigers and, say, zebras? Is that the same mechanism for cat, tiger and zebra or an unrelated one? One would guess that in tigers and tabbies it would probably be the same, but that it might be a different one for zebras (and we don’t even mention cuttlefish).
Maybe it is a sound thing in the video, cat-rap?
I’m deeply impressed with the ‘low five’ in no 3. One can nearly *see* this cat thinking: “ag, there is that kid again who wants a low five… come one, let us be nice and give him (her?) one..little things, little minds…”
Harry is a beaut of a kitten.
Cat coat genetics are good for illustrating many principles of genetics. We used to use a program for simulation of cat mating to teach Mendelian inheritance at a university I where I formerly taught. The piebald and dilute gene loci (the latter noted by LDueck) exert effects on other gene loci, overriding their effects on the phenotype, a phenomenon known as epistasis. Furthermore, though the allele for piebald is dominant to not piebald, it is less evident in the phenotypes of heterozygous individuals (those having one copy of the dominant allele and one copy of the recessive), rather than being expressed identically to the homozygous dominant, and so is an example of incomplete dominance.
Something just occurred to me.
In most species, coloring is used for camouflage, to warn potential predators of toxicity, or to attract mates.
And, in most species, there’s not much variation between individuals.
In cats…I can’t for the life of me think of what purpose the coloring serves, and there’s huge variation.
Anybody know of any explanations?
Of course, domestic cats are closely related to the wildcats which, as I understand, are generally exclusively tabbies. Is it human domestication that’s created the colors? But we’ve recently discussed here the relative lack of domestication of cats….
b&
It serves human pleasure. Apparently every single cat mummified by the Egyptians was a tabby, identical in pattern to the wild ancestor, but this was already several thousand years after they had been domesticated. From what I read, humans selected color variants fairly recently, and they probably persist in feral cats because a. feral cats don’t live in a truly wild situation, and can scavange for food (also, there aren’t many predators) and b there’s a lot of gene flow between non-tabby house cats and feral cats as well. I suspect that if domestic cats became truly feral, living in the woods, say, they’d revert to tabbies, the cryptic pattern.
Makes sense — thanks. And that’s news to me that we know that the Egyptian mummy cats were tabbies. That being the case, it makes me wonder if we have the records to be able to trace the development of the non-tabby coat patterns…could be some interesting research to be done there, if it hasn’t already been done. I’d love to know how recently the various major patterns arose.
b&
Color variants regularly emerge in animals, and we would select for them. Most variants would not confer fitness in the wild, but they would be offered up on a regular basis anyway. Humans would selectively breed them as a novelty, or as a way to recognize our animals.
It is interesting that that the piebald coloration is exceedingly common, and is seen is pretty much all mammals. The well known selective breeding experiment on foxes in Russia had produced piebald foxes rather quickly. There are also piebald humans that turn up in African populations.
Again, makes sense. Thanks.
b&
I’ve wondered about this, long before I understood anything at all about genetics. As a whole, the apes are a fairly monochromatic bunch. Why is that? And if color patterns can arise without chimerism, why is it so uncommon?
Were the Egyptian cats tabbies?!?
I always figured them like Abyssinians, I mean these statues don’t indicate any stripes, which of course doesn’t mean very much. (I’ve been told that those beautiful classic greek white marble sculptures were actually painted in their time, something I’ve difficulty to cope with.)
No, the book I just read on cat behavior and biology, “Cat Sense” (recommended) says that every single mummy cat that was examined was a tabby. The abyssinians definitely came later, as did all non-striped domestic cats.
I find that awesome, that after thousands of years we can *know* now they were tabbies and, as you gathered, I’m a kind of tabby fan (haven’t read the book, but suppose the evidence is solid).
Ferals in the Australian bush tend to be really feral, many generations away from suburbia, and subject to predation by dingos and eagles as well as needing to sneak up on prey; I’ve often seen black, tabby and ginger, a couple all-white and one or two torty, but no piebald or calico. The white ones were in the Blue Mountains west of Sydney (but still tens of km from any town), so possibly hadn’t been under selection for crypsis for as long.
Thanks for the biology Professor Ceiling Cat!
Very interesting indeed.
Are torties more rare than calicos? Common sense tells me that since calicos also need the piebald gene, that perhaps they are more rare.
I knew about Klinefelter syndrome, but thought it was much rarer than 1 in 1000. So is an XXY combination a possibility for all life-forms with XY chromosomes, or is it exclusive to mammals?
This seems to imply that the sizes of the coloured patches on a tortie’s fur depend on when the extra X chromosome was deactivated in its embryonic development; later deactivation should correspond with smaller patches
Yep, that’s right.
Very interesting post!
What a great post.
Evolution and cats and I have a female tortie who is the sweetest little cat you could wish for.
With one exception *all* the cats in my life have been of the striped variety. Miniature tigers, I would always go for the striped one in the litter (Cf Handel’s “with His Stripes We are Healed”, not only one of the most beautiful chorales in his ‘Messiah” , but one of the most beautiful pieces of music ever written full stop).
My last kitty was a Calico male (so I guess a Klinefelter), he was the most extraordinary kitten I’ve known. He really forced himself on me -I mean he even snuck into my car when I was leaving the place where I had been camping (where he had been constantly been invading my sleeping bag), and was the most affectionate kitten ever. Sadly the huskies next door killed him. Thinking of him I’m literally crying now. I decided never to have a cat again.
Oh dear. Damn d*gs. So sad.
The Oatmeal’s “cat’s Schrodinger” is awesome, yet we know before opening the box he’s dead 🙂 .
Great post!
We currently have a dilute calico, a tortie, & a gray tiger. The tortie is a force to be reckoned with.
Sub
From my experience with cats, I suspect the cat likes the sound of the paper flicking back. Cats like high pitched noises that sound, I presume, like small rodents. We have a number of Mylar roses which the cats love, they make a sort of rustling noise which they seem to find irresistible.
Fascinating post – I really understood that! About 25 years ago my late wife and I got three kittens from that self-same cat shelter in Bonnyrigg. Sadly, they are all gone now, but it’s good to hear that the rescue centre is still going strong.
I thought I already understood the difference between calico and tortoiseshell, but I was clearly confused. Now I may be more confused.
As a side note, one of the things I enjoy about this
blogwebsite is that I have to keep a dictionary handy (two words, just in this post).Oh no! More confused! Just think of calicos as tortoiseshell cats with an extra gene form that gives white coloration. For that’s all they are.
Ah, I think I’ve got it now. To outward appearances, then, there is a continuous spectrum between tortie and calico, is that correct? (I’m mentally picturing various of my local neighborhood kitties.)
More or less although there are only two types of gene combinations adding the white (S/s and SS). But those combinations each show variability, giving a more or less continuous amount of white.
What a wonderfully informative post — & comments. I was not aware that Egyptian cats were tabbies (although I have Cat Sense, it’s sitting on my shelf awaiting completion of my thesis)!
For what it’s worth, judging by manuscript depictions, coat variations in domestic cats existed by at least the medieval era (see the list below for a very small sample). So, perhaps we started selecting for coat colour in the pre-medieval era, at least.
As an aside, if anyone is looking for a unique gift for their favourite ailurophile, medievalist Kathleen Walker-Meikle’s lovely little volume Medieval Cats (British Library, 2011. http://www.amazon.com/Medieval-Cats-Kathleen-Walker-Meikle/dp/0712358188) might fit the bill. Walker-Meikle has also recently published Medieval Pets (http://www.amazon.ca/Medieval-Pets-Kathleen-Walker-Meikle/dp/1843837587), & Medieval D*gs (http://www.amazon.ca/Medieval-Dogs-Kathleen-Walker-Meikle/dp/0712358927) — though I cannot imagine why any sane person would want the latter volume.
Depictions of Cats in Medieval Manuscripts
BLACK / GREY:
– Bestiary. England, 13th cent. Bodleian, MS 533, fol. 13r. https://41.media.tumblr.com/14581174a3548ab5454ca84d98b0cf74/tumblr_mucsetm6gK1rqxd5ko1_500.jpg
– Vincent of Beauvais’ Le Miroir Historial. Paris, 1400–1410. Den Haag, Koninklijke Bibliotheek, MS. 72 A 24, fol. 313v. http://www.cathar.info/pics/cat.jpg
ORANGE:
– Book of Hours. France, 15th cent. Beinecke, MS. 662, fol. 21r. Catalogue: http://brbl-dl.library.yale.edu/vufind/Record/3446481. Image: http://media-cache-ec0.pinimg.com/736x/2d/5a/43/2d5a437751100c3afd9fe651ab5dc19f.jpg
WHITE:
– Thomas of Cantimpré’s Liber de natura rerum. France, ca. 1290. Valenciennes, Bibliothèque municipale, MS. 320, fol. 72r. http://media-cache-ak0.pinimg.com/736x/1f/cd/7d/1fcd7dbf60432a67c3e6cc87a9e72f2b.jpg
– Sextus Placitus. De medicina ex animalibus. England, late 12th cent. Bodleian, MS. Ashmole 1462, fol. 58v. http://bestiary.ca/manuscripts/manu8067.htm
– The Fables of Bidpai in German tr. Wurtenburg, ca. 1480. Musée Condé, Chantilly, France, MS. 680/1389, fol. 96. http://www.bridgemanart.com/en-GB/asset/60193/German-School-15th-century/Ms-6801389-f.96-A-Cat-Catching-a-Mouse-from-the-
STRIPED:
Brown:
– The Ormesby Psalter. England (E. Anglia), ca. 1300–1310. Bodleian, MS. Douce 366, fol. 131r. http://bestiary.ca/manuscripts/manu5450.htm
– The Ashmole Bestiary. England (Peterborough?), early 13th cent. Bodleian, MS. Ashmole 1511, fol. 35v. http://bodley30.bodley.ox.ac.uk:8180/luna/servlet/view/all/what/MS.+Ashmole+1511
– The Harley Bestiary. England (Salisbury?), ca. 1225–1250. British Library, MS. Harley 4751, fol. 30v. http://www.bl.uk/catalogues/illuminatedmanuscripts/record.asp?MSID=8797&CollID=8&NStart=4751 (scroll down & click the thumbnail).
White:
– The Ashmole Bestiary. England (Peterborough?), early 13th cent. Bodleian, MS. Ashmole 1511, fol. 35v. http://bodley30.bodley.ox.ac.uk:8180/luna/servlet/view/all/what/MS.+Ashmole+1511
– Bestiary. England, ca. 1225–1250. Bodleian, MS. 764, fol. 51r. Description: http://bestiary.ca/manuscripts/manu1085.htm Image: http://media-cache-ak0.pinimg.com/736x/45/b9/4c/45b94cd3b6270e5f255db19e64042dff.jpg (incl. black cat)
Silver:
– The Hours of Charlotte of Savoy. Paris, ca. 1420–1425. Pierpont Morgan, MS. M.1004, ff. 125r, 165r, 172r. Catalogue (navigate to images from here): http://utu.morganlibrary.org/medren/Manuscript_images.cfm?ACC_NO=M.1004&StartRow=1 [A particularly interesting juxtaposition is f. 172r — the text alongside the cat is John 6:54 😁]
– The Luttrell Psalter. England, ca. 1325–1340. British Library, MS. Add. 42130, fol. 190r. http://www.bl.uk/manuscripts/FullDisplay.aspx?ref=Add_MS_42130
Blue:
– Book of Hours. England, ca. 1300. Walters Art Museum, Walters MS. W.102, fol. 78v. http://www.thedigitalwalters.org/Data/WaltersManuscripts/html/W102/description.html
– Psalter. England, ca. 1210–1220. Bodleian, MS. Ashmole 1525, fol. 40r. http://bodley30.bodley.ox.ac.uk:8180/luna/servlet/s/04h73a
Black / Slate:
– Theological miscellany, incl. Summa de vitiis. England, ca. 1236–1275. British Library, MS. Harley 3244, fol. 49v. http://www.bl.uk/catalogues/illuminatedmanuscripts/record.asp?MSID=8798&CollID=8&NStart=3244
– Ashmole Bestiary. England (Peterborough?), early 13th cent. Bodleian, MS. Ashmole 1511, fol. 35v. http://bodley30.bodley.ox.ac.uk:8180/luna/servlet/view/all/what/MS.+Ashmole+1511
SPOTTED:
– Gaston Phoebus’ Livre de la Chasse. Paris, c. 1407. Pierpont Morgan, MS M.1044, fol. 27. http://www.themorgan.org/collection/livre-de-la-chasse/13 (also incl. black or slate coloured cats)
– Breviary. Italy, Apulia (prob. Taranto), 1350–1400. Pierpont Morgan, MS. M.200, fol. 462v. Catalogue: http://corsair.themorgan.org/cgi-bin/Pwebrecon.cgi?v1=14&ti=1,14&Search%5FArg=Breviary&Search%5FCode=GKEY%5E&CNT=50&REC=0&RD=0&RC=0&PID=oB4cCPzXg2LbwzpQ5AA9_rtCNlgQ&SEQ=20140228065139&SID=1. Image: http://utu.morganlibrary.org/medren/single_image2.cfm?imagename=m200.462vc.jpg&page=ICA000191139
… &, for fun, “Grumpy Cat is a Time Lord”: http://senseshaper.com/the-medieval-and-early-modern-meme-menagerie-or-grumpy-cat-is-a-timelord/
Is your thesis by any chance on cats?
No! (Sometimes I wish it was…). I love (inter al.) lists, books, & cats. A few years ago, I started keeping a list of cats in medieval manuscripts (thereby combining the three). Cats crop up in medieval texts with surprising frequency — they were a bit of a necessity, to keep down the vermin.
Such a fascinating hobby!
Any animal drawn in the mediaeval period is worth a read! I love how medieaval artists drew everything & animals are particularly cute to look at.
Medieval art tends to have a really unique aesthetic, doesn’t it? I enjoy it, too — particularly the bizarreries such as the snail-cats (e.g., fol. 185 here: http://www.bl.uk/catalogues/illuminatedmanuscripts/record.asp?MSID=8020&CollID=21&NStart=17) which are more common than you’d think.
Rabbits always seem to have a peculiar look too. The couple I saw from the page with the snail cats you linked to (never saw snail cats before & they do seem to be very cool looking) seem to have rather devious faces. I don’t think mediaeval people totally trusted rabbits!