This article is from the Summer I 1997 AFRMA Rat & Mouse Tales news-magazine.

By Ann-Zophi Pålsson and Eva Johansson, Sweden—genetics is fun!

ED. NOTE: This wonderful article was sent to us as part of the Tamråttans Vänner Yearbook. I found it extremely intriguing, and as permission was granted to reproduce it, we thought we would share it with everyone. The “Safir” color equates to our Mink and Lilac. As is pointed out in the article, this color can be bred to be a light pastel brown (Lilac) or a dark almost chocolate with a blue cast (Mink). In an upcoming issue, we will be reprinting Ann-Zophi and Eva Johansson’s article on “Honung” (Cinnamon Pearl)

One day several million years ago, well . . . anyway in the beginning of the 20th century, a new mutation appeared with the fancy rat, a gene that gave a colour that today is called Safir. A good Safir is a greyish-brown rat with a blue hue, without white hairs or tinges in the fur and has black eyes.

Safir has been a colour that has caused a problem for a long time; it has seemed difficult to identify it with the correct gene. Many theories existed on how the genetics worked to make a Safir. The variety has changed names a couple of times. The first name was Blue, the second name was Mink, and the third is Safir.

When a new colour appears, you cannot be sure straight away if there is a question of a new combination of already existing genes, or if there is a question of an altogether new gene that has shown up. All new colours do not stem from new mutations (e.g. new genes that appear and take over to decide the colour of the rat). Usually, there are old genes in a new combination that produces the new colours. In the beginning of the 20th century, there weren’t that many known colours on the rat. There was Albino, Viltbrun (=Agouti), Svart (=Black) and Brandgul (=Silver Fawn). The first trace of Safir appeared when a bluish rat turned up around 1905, and this rat colour was given the name Blue because of its blue-grey colour. We should divide the domesticated rat in two groups: Group 1 is the domesticated rats that are used in animal tests, the laboratory rat. Group 2 is the domesticated rats that amateur breeders and fanciers breed, namely the fancy rat. These two groups were sometimes isolated from each other and no exchange of genes (e.g. different heredity traits), took place. This led to the fact that many new varieties or mutations appearing in the laboratory rat never crossed over to the fancy rat.

In 1935, the two geneticists Castle and King wrote about a gene in the laboratory rat that they called Fawn Dilute. This gene could be the same gene that was found in the fancy in 1905. The Fawn Dilute gene will give a coffee-brown coloured rat and combined with the d-gene, a colour called Lavender. Fawn Dilute was an analogue gene to the Chocolate gene according to Castle and King. It rather looks as if they had succeeded in combining the Fawn Dilute gene with the Chocolate gene, hence all the colours that appeared. Further you can read a lot of confusing data about Blue in the literature. The colour Chocolate was at some time to be changing its fur and become Blue?!! Blue seemed to be wished to be Chocolate and vice versa. Another thing is that Mink Agouti (called Cinnamon in most standards) had the name Fawn Agouti in the beginning. Does this show that it is the Fawn Dilute gene behind this colour?

In 1977 Blue was standardized in England, but first its name was changed. The new name was to be Mink. The cause of the change of names can be that the real Blue gene (d), corresponding with blue in several other species, is known on the laboratory rat. Usually, a new gene is named something suitable that corresponds with what is thought that the new gene represents, and when the real gene appears, changes are made. For example, the hamster that earlier didn’t have a really black colour, but there was a colour that was called black. This colour wasn’t really black, but sable that was bred to be as dark as possible. One day, the real black hamster appeared and the colours were renamed and also, changes on the thoughts about the genes responsible for the involved colours were made. Why the name Mink was chosen is not known, but there was another rat colour, also called Mink, namely a blackish-brown mink-looking colour (like Mink, the animal). This other Mink is a darker variety of chocolate (aa bb). Our Safir migrated under the name Mink to Sweden where it now is one of the most common colours (and the name Mink is also often used by some breeders). The discussion about which gene that caused the Safir colour went on. It was thought that Safir was Chocolate and Safir got the symbol b. (The symbol of Chocolate is b.) Chocolate suddenly was X. Very exciting! The gene that gives Safir could be an analogue to the chocolate gene and therefore Chocolate and Safir easily could become confused with each other. This could also explain the Safir-coloured rat’s greyish-brown colour. But this is not the end of the story!

The naming of colours is sometimes different on the laboratory rat than on the fancy rat. In naming the colours on the laboratory rat, the knowledge about the genetics is often very good. Different geneticists use different names for different varieties according to their genetical hypothesis, while naming the fancy rat is rather unchanged. The standards are not upgraded when new knowledge is learned about the genes involved. New facts about the rat appears all the time and usually the fancy is far behind. It takes time for new facts to get assimilated into the world of the fancy rat. There seems to be a strong tendency to believe in the old, long since rejected theories.

A simple test mating can directly show that Safir is not the same as Chocolate. Mate a Chocolate with a Safir and you usually get Black, that is the proof. If Safir had been a Chocolate variety belonging to the same series of genes, then there would have been all Safir or all Chocolate, depending on which is on top in the series. The geneticist Roy Robinson has decided to give the Mink gene the symbol m, which now is the symbol that most geneticists use.

Another funny genetic theory, or rather not funny, is that Safir and Blue should belong together, e.g. the real Blue (aaBBdd) and Safir (aaBBmm). Since Safir once was called Blue and furthermore looks Blue, it could easily be a question of an allele to the d gene. Safir x Blue should then only give Blue or Safir depending on which is highest in the series. But I happily made a test mating between Safir and Blue and this gave Black, which proves that we, in the fancy, have two diluting genes that gives blueish rat colours, the d gene and the m gene. (Before this the d gene only existed on the laboratory rat.) Instead of being an analogue to the chocolate gene, the m gene is an analogue to the d gene.

When the name Mink did not give justice to the colour, Tamråttans Vänner renamed this colour to Safir. Safir is a much more suitable name, since Safir in other species is used for blue coloured animals. Safir is Swedish for sapphire.

The gene that is causing all this, is a gene that bleaches the pigment (e.g. in reality, the gene changes the size of the pigment granules and their placing). Our eye interprets this as bleaching. Since we changed the name of this colour, it could have been in place to also change the symbol of the gene and call it the s gene (s for Safir).

The interesting thing here is that the m gene or Safir gene (or whatever we finally decide to call it) bleaches Chocolate to a warm, somewhat red hue milk-chocolateish colour (that we like to call Mahogany). This can be the cause for the confusion and the belief that Chocolate and Safir (Mink) should be the same, or that Chocolate should be Safir, or that Safir should be Chocolate, and other funny theories.

Another very nice thing is that we can combine the colour Blue with the colour Safir and get a totally new colour called Himmelsblå (sky-blue) which then is a doubly-diluted black rat.

Safir rats which aren’t colour bred can have a brown hue depending on the presence of polygenes of the Rufus group and can be generally less in the same hue all over just because they are not colour bred. When the breedings have been going on for about five generations, true bred Safir darkened the colour somewhat, made it more solid, deep, and beautifully blueish, then you clearly understand that Safir really is a colour of its own.

The recognized symbol for the actual gene is today m and all rat societies, except Tamråttans Vänner, call the colour Mink or Self Mink. New information that I found says that the Fawn Dilute gene exists; I wonder where it is and what the colour looks like, that this somewhat mysterious gene gives? For instance, a coffee-brown rat, could that be a café au lait colour or does it look like dark almost black coffee?

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