American Fancy Rat & Mouse Association

This article is from the Summer 2002 AFRMA Rat & Mouse Tales news-magazine.

Colors & Coats

Siamese Mouse Formula

By Nichole Royer

Katherine Garcia, Corpus Christi, TX
QI am presently living in South Texas where it is very frustrating because the typical idea of an exotic pet is a snake and mice are nothing but reptile food. I have been breeding fancy mice for over a year and have managed to breed my own black and white pieds, long haired golden pieds, and finally Chocolates with the introduction of a Silver stud. I am now interested in Siamese. I can’t seem to get anything but blank looks and head shakes—not even a decent book!

Could you please tell me of a breeding formula for Seal Point and Blue Point Siamese mice.

AThe Siamese pattern in mice is a favorite among both fanciers and pet owners alike. This color is a relative newcomer and was first reported in the scientific literature in 1961. These mice are very pretty and rather striking looking. The AFRMA standard describes them as: “The Seal Point Siamese mouse is to be a warm beige, as even as possible over the entire body, shading to a deeper color on the hindquarters. The colors should blend gradually and there should be no white hairs or mealiness to the color. The points should be a rich chocolate color and should be well defined on the muzzle, being confined to the whisker area only. The ears, feet, tail and tail-root are dark also, but are of a slightly lighter shade. Eye color may be ruby or black.”

The traditional Siamese pattern of dark points on a lighter body is caused because the color is thermo-sensitive (the fancy word is acromelanism). This means that the color of the fur is determined by the temperature of the skin where it is growing. The fur on the warmer parts of the mouse’s body grows in lighter, and the fur on the cooler extremities (feet, nose, ears, tail) grows in darker.

Please understand that you cannot “create” Siamese mice from scratch. This color is not caused by a combination of other colors, but is instead caused by a specific gene. Without that gene you cannot produce any Siamese mice.

The first step in breeding Siamese mice is to get your hands on one in the first place. Sometimes this can be the biggest challenge, particularly in areas where fancy mice are hard to come by.

The gene that causes the Siamese coloration is the “Himalayan” gene ch. When a non-agouti aa mouse inherits one ch gene from each parent, the result is what we call Seal Point Siamese aachch. Once you have two Siamese, they can be bred together and will produce all Siamese babies.

If you get your hands on only one Siamese, your best bet for producing more is to breed to a nice Black Self. The resulting offspring will be all Black; however, if they are bred together, they will produce Siamese.

Once you have Siamese, there are many things you can do with it. Breeding Siamese (aachch) to Pink-Eyed White (albino aacc) will produce a litter of all Himalayans (aachc). The addition of the albino gene causes the color of the Siamese to lighten and the result is Himalayan which the standard reads: “The Himalayan mouse should be as nearly white as possible over the entire body, with well-defined points, as for the Himalayan rabbit. The points are to be a light milk chocolate. Eye color is red or ruby.”

On the other end of the spectrum, the addition of Chinchilla (cch) to Siamese darkens the color and produces Siamese Sable. This is a rather spectacular color described as: “The Siamese Sable is to be a very light brown similar to the coffee, over the entire body. The points, which are a very dark brown, almost black, are as for the Siamese. Eye color is black.” The best way to create Siamese Sable is to breed a Siamese to a Black Fox (or any non-agouti Fox other than a Beige Fox). You will see Siamese Sable in the first generation. You can also produce this color by breeding to a Chinchilla mouse, but any Siamese color on an Agouti background will be mealy. It is best to stick to non-agouti based Siamese whenever possible.

One of the most popular combinations with Siamese is the addition of Blue to produce Blue Point Siamese. They are Blue Point Siamese Mouse very pretty and the AFRMA standard describes them as: “Color to be a silvery blue (bluer the better), as even as possible over the entire body. The shading to be gradual over the saddle and hind quarters and being darkest at tail root. The belly should be as near as possible in color and shading. The points (nose, ears, feet, tail, and tail-root) to be a medium slate blue. There should not be a definite or distinct line of demarcation but rather a toning in or merging with the remainder of the coat. There should be no white hairs, blotches, streaks or mealiness of the color.”

In order to make Blue Point Siamese (aaddchch) you must first have two things, a Siamese mouse (aachch) and a Blue mouse (aadd). Once again, if you live in an area where some of the colors can be hard to come by, this will be your greatest challenge. Breed the Siamese to the Blue and in the first generation, you should get black offspring which carry Blue and Siamese (aaDdCch). Breed these together and you should get Black, Seal Point Siamese, Blue, and Blue Point Siamese. The genetic probability of getting Blue Point Siamese is only 1 in 16, however, so it may well take more than one litter for it to show up.

As with the Seal Point Siamese, there are many variations you can create with Blue Point Siamese. These can be created just as you did for the Seal Point Siamese, with the addition of the dilute gene (dd) better known as Blue. Just like with the Siamese Sable, Blue Siamese Sable are created by adding the Chinchilla gene (cch). The Standard says: “The Blue Sable Siamese is to be a medium blue, similar to the Self Blue, over the entire body. The points, which are a dark blue, are as for the Blue Point Siamese. Eye color is black.” You can also produce Blue Point Himalayan by adding albino (c). *

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Updated December 28, 2014