# We are Siamese if you Please



## Alan_Calderwood (Jul 17, 2009)

*found this interesting article on the Siamese gene linking coat colour density to temperature i am not sure if this applies to mice or not but its an interesting read *

This Siamese cat, raised in a cold environment in Moscow in the late 20s, developed a relatively dark coat. An area on his shoulder was shaved, and the cat wore a warm jacket while the fur was growing back. When the shaved hair grew back in, it was white, the same color as the cat's belly, due to the increased temperature under the jacket. This was not due to scarring, as the hair grew in normally colored later.

In the genetic code of Siamese cats, Himalayan rabbits, and certain mice lies a mutant gene that produces the special pattern of color in these animals. Not only does this gene restrict color to areas which are cooler than normal, it affects the organization of the brain as well.

The Siamese gene is thought to be one of a series of genes, called the albino series, that participate in the formation of melanin pigment. In its normal form, which is completely dominant over all of its other forms, it allows full expression of whatever genes for color the animal may possess. In its most recessive form, the albino gene, no melanin-type pigments can be formed in the pigment-generating cells. An animal or person with two albino genes will have white or light reddish hair, pink or red eyes, and a white to yellowish skin which will appear pinkish due to the blood showing through. (Some color will remain from other, non-melanin pigments such as the hemoglobin in the blood, especially in individuals whose normal pigment would be very dark.)

Some intermediate forms of the albino gene prevent the synthesis of phaeomelanin (red-yellow melanin) and variably lighten the color of eumelanin (black and chocolate brown melanin). The "albino" tigers seen in some zoos, with brownish stripes on a white body, are due to this type of "chinchilla" gene, which is recessive to full color but dominant to albino.

The Siamese or Himalayan gene is recessive to chinchilla and to full color but dominant to albino. It is unusual in that it can only produce pigment at temperatures below normal body temperature for mammals. Thus the body coat of a cat with two Siamese genes is very light in color, as the Siamese process of melanin production is very inefficient at the normal skin temperature of the trunk. The legs, ears, face and tail, however, normally have skin temperatures several degrees colder than does the central body. These areas can and do produce whatever pigment the other color genes carried by the cat permit at only slightly less than normal intensity. An ordinary seal-point Siamese, for instance, is genetically black, while a chocolate-point has brown genes similar to those in a chocolate Labrador.

One result of this is apparent to people with Siamese pets that get into fights and spend time outdoors in the colder months of the year. If a Siamese cat loses a tuft of fur from the body in cold weather, the skin where the fur is missing will be much colder than normal until the new fur grows back, and the outer part of the replacement fur will match the legs and face rather than the normal body coat.

Coat color isn't the only thing affected by the more recessive members of the albino family of genes. Siamese cats have a reputation for being cross-eyed, and the peculiar organization of their visual nervous system may be the reason. In a normal cat, nerves from each eye go to both sides of the brain. In a cat with two Siamese genes, the nerves from the right eye go primarily to the left side of the brain, and those from the left eye go primarily to the right side of the brain. This anomaly probably causes the cross-eyed appearance of many Siamese cats. Judging from their jumping performance, however, their depth perception is good, so they are somehow compensating for their abnormality.

Related information is available on banded (agouti) hair, overdominant dilution genes, and white spotting in domesticated animals.


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## Rowangate (Jul 28, 2009)

In rats a siamese that is kept in a colder environment ie a shed compared to being indoors with central heating will have better/darker shading on the rump, nose & feet points compared to the latter. Although if genetically the points and shading are pale they will never be the required shade for the show bench.


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## SarahC (Oct 3, 2008)

It is accepted that siamese mice are better as a show animal when kept in colder temperatures.This is purely from the aspect that as an exhibition animal their coats are frequently ruined by moult marks.Cold = less moulting.Getting a siamese on to the show bench without this heavily penalised fault is a challenge.You could put the theory of darker points in winter to at least two people I can think of who attend shows and will be at Preston.My own opinion is that the dark points are selected for and cold temperature won't make much difference.


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## Oca2 (Jan 1, 2009)

Yes, the color/temperature relation applies in mice too. The siamese mutation in c-locus makes the gene product tyrosinase heat sensitive. That's why tyrosinase has decreased activity in the trunk, but in the colder regions of the body this more fragile form of tyrosinase can still work.

Recently I was discussing the subject with a family member; he suggested that maybe by breeding siameses with better points we are breeding mice with poor circulation, i.e. mice with cold feet. :mrgreen: This is of course a strictly unscientific hypothesis.


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## SarahC (Oct 3, 2008)

lucky you having a family member willing to talk about cold feet in mice :lol:


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## vickyholt13 (May 30, 2009)

its same in guineas the himilayans colour is darker and richer in the winter and tends to look faded in the summer.


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## Oca2 (Jan 1, 2009)

^^ I am.  It goes both ways though, me being willing to talk about whatever caughts their fancy - and of course, keeping the genetics talk to a reasonable lenght. Apparently there is only so much an ordinary person can endure.


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## Alan_Calderwood (Jul 17, 2009)

SarahC said:


> It is accepted that Siamese mice are better as a show animal when kept in colder temperatures.This is purely from the aspect that as an exhibition animal their coats are frequently ruined by moult marks.Cold = less moulting.Getting a Siamese on to the show bench without this heavily penalised fault is a challenge.You could put the theory of darker points in winter to at least two people I can think of who attend shows and will be at Preston.My own opinion is that the dark points are selected for and cold temperature won't make much difference.


as said i found it quite an interesting read as ive been trying to learn as much as i possibility can about the Siamese/Himalayan gene (pew as well) as those are the variety's i am hopefully going to be keeping 
i agree with you on the fact that selection of plays a bigger role in the quality of the points rather than how the gene is affected by temperature but i think its something worth investigating and considering ....maybe people have been keeping there Siamese cool to improve there coat quality and unknown to them have been improving the points as well

just a thought...dose any one know if in a Siamese as the points darken is there a tendency for the rest of the coat to lighten or darken


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## Kallan (Aug 16, 2009)

The temperature link is known in cats - when we have to clip a pointed cat e.g. for a blood sample/surgery, we have to warn the owner that the fur may grow back darker!


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## Mari (Jul 21, 2009)

I know rats will develop more/darker shading throughout the body as their points darken while kept cooler.


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## violet1991 (Oct 3, 2008)

vickyholt13 said:


> its same in guineas the himilayans colour is darker and richer in the winter and tends to look faded in the summer.


or rather, the points are very nice in winter, body colour goes pants because it too darken, and in summer body colour is often fab and points go downhill.... never ending battle. I time my litters on this sometimes. babies born in the summer will have worse points than those in the winter, but will maintain a good body colour, those born in the winter will often maintain good points, but have awful body colour. Temperature is VERY much a factor with himalayans i believe of any species.

also the albino thing....In guineas there isn't anything truely albino, and the himalayan is the closest to it, as mentioned in that article there, himalayan is albino with another gene that lets colour through on the extremities. though with guinea pigs it wont let yellow series colours through, hense why there are only black and chocolate himalayan cavies around. (some people are trying slate and beige, but they're gonna need a lot of work!)

I breed himis, so i HOPE that is all correct!

as for the mice, it's interesting to know it's almost the same thing!

Vi x


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