Caturday felids: We are Siameses if the environment pleases

One of the best examples of “gene-environment interaction” is the gene (allele) producing the coloration of Siamese cats.  The expression of this gene depends heavily on the ambient temperature that the skin experiences while the fur is growing. Cat World describes it (read this web page for a lot more information, particularly if you have a Siamese or Himalayan):

Siamese cats carry a gene known as the Himalayan gene. This gene is seen in other species, such as the rabbit and the mouse. It is a mutation at the C locus and it causes partial albinism. This gene is recessive to the full colour C gene.  This means you need two doses of it (homozygous) for the Siamese colour to show up. If you mate a Siamese to a Siamese, you will get Siamese offspring. If you mate a Siamese to a black cat, you will get black offspring which will carry one dose of the Siamese (cs) gene at the C locus.

The Burmese also shares the same type of gene, which is known as cb.

The cs and cb genes are co-dominant and hence if you mate a Siamese (cs) to a Burmese (cb) you will get a Tonkinese (cs/cb), which has “mink” colouring.

This gene is heat sensitive, the cooler the area, the darker the colour. Which explains why a Siamese has dark extremities such as the face, tail and legs. The body being the warmest part of the cat remains lighter in colour. You will notice your Siamese get darker in the winter months, especially if your Siamese is an indoor/outdoor cat.  Siamese cats are white at birth, this is due to being in the constant warmth of the mothers womb. This colouring varies from Siamese to Siamese.

Courtesy of my friend the British geneticist Steve Jones, here are three pictures of Siamese cats that experienced different temperatures:

First, a “normal” Siamese:

 

Siamese

Next, Siamese living in a cold environment.  Note the heavy dark pigmentation appears more widely over the body:

darksiamese

This is a Siamese living in a hotter climate.  It’s almost white, and note the tabby-like pattern that now appears on the tail:

whitesiamese

Finally, someone has shaved his initial into the side of this cat, which then re-grew the fur under cold conditions.

Esiamese

15 thoughts on “Caturday felids: We are Siameses if the environment pleases

  1. The red tabby or black is due to the other genes, not to temperature; the stripes have to do with the genotype for red, not with temperature. The genes non-agouti (A agouti, a non-agouti) and orange ( OO red female Oo red/black how depends on background oo red OY black or grey male oY red male) are relevant here.
    Siamese with black markings are cscs aa OO, where as the red siamese should be cscs AA oo or cscs Aa oo of cscs aa oo if female. Apart from lessons about plasticity, cat colours show good examples of epistasis. In three-color cats, aa Oo females moreover with white patches, the orange patches show stripes and the black patches don’t.

  2. I’m fascinated #4! My cat, Cleo, came from the local shelter. They claimed she was part Siamese.

    She is striped with gray and is beige where not striped. She has blue eyes which is why they assumed she was Siamese, I suppose.

    I guess it’s possible she does have a Siamese parent.

  3. We bred a Siamese to a black Persian, and got (color-wise) 2 seal-point Siamese, 2 lilac-point Siamese, and one all-black. Interestingly, the ones with Siamese colors got the Persian body-style, while the black kitty had the slimmer Siamese build.

    There may be differences between the darkness of the colors in the winter and summer coats, but it’s less than the differences between lilac-point versus seal-point….

  4. I have 2 Siamese that supposedly had a Siamese father and a black mother (I never saw either parent when I adopted them). The coloration on both of them is intermediate to #1 and #2 above, but closer to #1. One of them also has a big fluffy tail and has longer, softer, fuzzier fur than the other who looks pure bred and, apart from being a little smaller and chunkier, is a dead ringer for #1.

    The “pure” looking one also is an avid fetch player (albeit indoors with the little foam balls you can buy at Petco) and can out-fetch most dogs I know. I am hopeful to get full video evidence of this and submit it for consideration for Caturday Felids if I am ever able.

  5. Our previous cat, the very dignified Shelley, was half Siamese. His colour was entirely brown tabby, the commonest “wild” type. His ancestry showed in two, or perhaps three ways: he had a squalling, penetrating voice; he was very muscular without being stocky; and he was unusually smart.

  6. That’s so neat; if I had a siamese cat I’d shave a decorative pattern and let it live in the cold laundry room for a few weeks in the middle of winter. Erasable tatoos – no one else will have a cat like it.

  7. I knew about the dark coloration at the extremities, but I always wondered why our Birman in Chicago was noticeably darker on her back than her brother in NC. She does spend a lot of time outside. (under supervision)

  8. I live in thailand and although the temperature is tropical all the siamese cats I have seen are the standard colour even when not living in airconditioned environments. How hot does it have to be to be to remove the extremity darkness?

Comments are closed.