As you may have noticed, Maxwell and Faraday kind of look alike – Maxwell's
a Siamese and Faraday’s a Tonkinese. The pointed nature of their coats – darker
in the paws, tail, ears – is one of their most striking features.
 |
| Faraday (left) and Maxwell |
If you
discount Faraday’s lungs, that is.
 |
| Gratuitous shot of Faraday using his lungs |
Interestingly, that pointed coat is a form of albinism.
Wait...da boyz
are albinos? Say it isn't so!
Okay, it's not so – at least not the way an albino is traditionally
understood. When we think of an albino, we usually think of someone without pigment.
Well, da boyz aren’t stark white, so what gives?
Warning: geeky
scientific post ahead!
Well, it’s kind of a genetic thing. See, a cat’s coloring is determined by a
set of eight different genes. They're what tell a black cat
to be black, or an orange cat to be orange. But Siamese, Burmese and Tonkinese cats
have something funky going on with one of those genes!
 |
| Pointed cats have alleles that determine their coat pattern |
Before we get to the funky part, first we need to talk about what a cat gene looks like. Cat genes are made up of alleles – an alternate form of gene – and each gene has two: one from mom cat and one from dad.
One special set of alleles in Siamese type breeds sends a command that inhibits pigment – in other words, albinism.
Not funky enough for ya? Well, that signal
only gets through to a kitty's fur if it's above a certain temperature.
So basically what this means is that Siamese, Burmese and Tonkinese cats are
temperature-dependent albinos. Kinda cool, huh!
How does it work?
Well, the alleles start sending out their "Stop the Color!" message around 38-39.2°C, which is a cat’s standard body temperature.
Anything lower than that and the alleles’ message is blocked and the color gene
can then do its color thing. Since a cat’s body is cooler around his ears, paws and tail ... that’s where the color begins to kick in.
How come these cats are born lighter and then darken as they age?
 |
| Ryker at 4 months |
It’s pretty warm in the womb, so all kittens with this special pair of
alleles are white throughout gestation. They pop out as white kittens too, but
once exposed to atmosphere, their extremities begin cooling. Once they hit that
critical temperature, those alleles that have been inhibiting the enzyme
responsible for pigment turn off and color begins to develop – on the ears,
paws, tail and face.
Someone questioned why the face – does that really compute? Surely the face is warmer than the extremities!
True, but we have a lot of holes in our faces: eyes, ears, nose, mouth (that
was my dad’s big argument, by the way, when I was a kid and wanted to pierce my
ears: “you don’t need another hole in your head!”).
All those cavities in the head account for enough of a drop in temperature
to let the color kick in. Notice Ryker's nose is darkest? Big breathing holes there! And at this stage, his paws were just beginning to get their dark brown color.
So let’s think about this for a second. If all it takes to make these cats “go
albino” on you is to increase their temp, what if you made Maxwell wear socks? Would his paws turn white?
First…good luck with that experiment. Be sure to let me know how that worked out for ya,
‘k?
Seriously, if you could actually keep them on him, then, well…the answer is yes. Because coat
color is lightened by high body temperatures and darkened by lower temperatures, the color can be altered by a bandage covering the fur, illness, even cold weather.
If you followed Ryker’s medical condition during his last year, you may have seen his “Bikini wax”, as
we called it (he called it The Great Indignity, but I digress.)
 |
| Ryker, immediately after being shaved |
The vet shaved a
4 inch swath around his lower abdomen for a sonogram, and it happened right before we dove into one of the
coldest winters on record in Kansas City. His fur grew back a shade darker. (He
didn’t think it was very funny.) Fortunately, as spring turned into summer, his
coat lightened once again.
 |
| Ryker, early summer. Dark area is beginning to lighten. |
"But wait!" I hear some of you say. "Siamese, Burmese and
Tonks aren’t the
only cats with points!"
True. And all of this information can be applied to them as well: Himalayan, Colourpoint, Javanese, Balinese, etc. So why specifically focus on Siamese, Burmese and Tonkinese in this article?
Blame the scientists. It’s in the naming.
See, the scientists discovered
two different alleles (TYR-G301R and TYR-G227W).
One
is more efficient at turning color off than the other.
 |
| Natural Mink Burmese: Wikimedia Commons |
The more efficient one
was found first in the Siamese cat, and so those science guys named it the
Siamese allele (pairs designated c
s c
s – the 'c' stands for color, 's' for siamese). The other was
found in the Burmese cat, and therefore bears its name (pairs designated c
b
c
b).
This makes total sense if you look at pics of both breeds.
Siamese have the
most contrast whereas Burmese can sometimes have very little contrast.
That’s
why many Burmese – and half of the Tonkinese – aren’t described as
points, as in “seal point” or “blue
point”.
They’re known as
minks instead. See how little contrast the guy in the picture on the right has? He's considered a mink, not a point.
Back to the other breeds for a sec: they also have allele pairs. Himalayans, for example, have the Siamese (c
s c
s) allele. Some Ocicats carry the Burmese allele.
And as far as Tonkinese go – well, guys like Faraday (a platinum mink) fall in
the middle. They have one of each, so a pointed Tonk will have a Siamese
dominant allele pair (c
s c
b), whereas cats like Faraday
who are minks will have a Burmese dominant allele pair (c
b c
s).
 |
Faraday's coloring isn't as extreme: he's a Platinum Mink
(Platinum name comes from coat sheen) |
Oooookay. Done with the hard science. Back to the cool stuff.
What if da boyz didn't have that allele pair? If you ignore the funky, temperature-dependent albinism thing going on...
Genetically, Maxwell's a solid grey kitty. Faraday's silver. And Ryker? He'd be dark brown.
 |
| Caleb: Seal Point Siamese = black cat (with alleles) |
Caleb, Ryker's older brother and a seal point Siamese – well, genetically he was a black cat... with alleles. Interesting to think about, no?
Next Week:
Temperature-Sensitive
Albinism and Eye Color
______
sources:
Anim Genet. 2005
Apr;36(2):119-26.
Tyrosinase mutations associated with Siamese and Burmese patterns in the domestic cat (Felis catus).
Lyons LA;Imes DL;Rah HC;Grahn RA.
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, CA 95616, USA.
lalyons@ucdavis.edu
http://www.ncbi.nlm.nih.gov/pubmed/15771720
"Ocular pigmentation in white and Siamese cats,"
Investigative
Ophthalmology & Visual Science, 1980 May;19(5):475-86.
Published by
NationalInstitute of Health's PubMed site
