American Fancy Rat & Mouse Association

This article is from the WSSF 2014 AFRMA Rat & Mouse Tales news-magazine.

Colors & Coats

Mouse Genetic Questions

By Karen Robbins

QI have a couple of genetic questions in regards to some varieties of mice. My wife and I currently breed English-type mice. I have always been fascinated with the huge genetic color diversity in mice. I have studied color genetics of mice for years. However, there are a couple of AFRMA varieties that I cannot figure out.

The first one being Gold. I have bred lethal yellows, Ay, in the past. So, I have had Reds, P.E. Fawns, and some mice that would fall into B.E. Fawn (though I always considered them to simply be bad Reds). We are now starting to work with recessive yellows, ee. With the recessive yellow, we are producing mice that fit the Orange and B.E. Fawn description as well as some very pretty but different looking Agoutis that don’t meet any standard. I have, however, never seen a mouse that fits the description of the Gold Standard, and I would like to.

Next, what is the difference between a Cream and an Ivory? The way I read the standards they are both the same, I am assuming aa cec, with the Cream possibly being slightly darker. But it does not seem to be enough of a difference to warrant two separate varieties, so I think I am misinterpreting the standards for the Cream and Ivory somehow.

Silver Black and Silver Gray, am I correct in my thinking that these are the Chinchilla version of Agouti and Blue Agouti minus the tan gene (A– B– cchcch D– P– and A– B– cchcch dd P–)?

Lastly, what are the genetics behind the Reverse Siamese? The few photos I have seen of this variety are very attractive mice. Though I am assuming that they don’t have the Siamese/Himalayan gene, ch, as the name implies. If I had to guess, I would say that it is a Coffee Fox Head Spot with modifiers for the hs gene (ata cece hshs). Am I even close?

I would also love to hear your take on the Roans and Merles. We have both, yet the breedings seem more like a crapshoot than anything. Never sure what is going to show up in those litters. In fact they are more random then our Head Spot (hshs) litters. We sincerely appreciate any information you might be able to provide us with.

I also wanted to add one more question. What are the genetics behind the Splashed? I have had some odd looking mice popping up out of our co-dominant c project, ch and ce gene combinations. These mice look a lot like what AFRMA defines as Splashed on their web site, only with fewer spots.

Gold Broken Marked mouse
A Gold Broken Marked Standard mouse owned and bred by Kelli Boka. Photo ©2007 Craig Robbins.

AGold is just a light version of Fawn (dominant yellow gene Ay). We had these many years ago in the 1970s and 1980s and no one breeds them any more, though we did see one at a show in 2007. It’s just a selection process. The recessive yellow/fawns (extension gene ee) are more popular with breeders since they don’t get fat or have other issues like the dominant yellow gene has. Read Bonnie Walters’ series of genetics articles for more on dominant yellow/fawn and recessive yellow/extension genes (found in the AFRMA Mouse Genetics book).

AFRMA’s Cream is Ay cchcch (Fawn + Chinchilla). Another way to make Cream is Fawn + Chocolate + Blue + P.E. (or a P.E. Dove/Lavender + Fawn Ay bb dd pp). AFRMA’s Ivory is England’s B.E. Cream cec (one ce gene—extreme dilute gene —and one PEW gene, c). When we brought in England’s B.E. Cream we already had the standard for Cream, and since the genetics are different and the color slightly different, we decided to keep both versions and give them the name of Ivory. The old Rat, Mouse, Hamster Fanciers (RMHF) club in San Francisco gave this color the name Bone as did some of the clubs in Europe. What England had done with theirs was to keep the same name but have a different genetic version (their Cream used to be the Chinchillated Fawn like ours). With the Cream mice, they have the same problems of obesity, etc., of the dominant yellow/Fawn where the Ivory don’t.

The Reverse Siamese is the homozygous/dark version of Ivory in the Beige (extreme dilute) family of genes (Ivory cec, Beige cece, Coffee cece, Reverse Siamese cece). In England they don’t show this color and call it Stone (dark Cream). We recognize both gene variations and the different shades. The English stock we originally got came with the lighter points and we made the Reverse Siamese standard from them. The Beige and Coffee we had previously did not have the lighter points. Again, it is a selection process for the different shades. If you select the Ivory/B.E. Cream to be very pale, you could have mice that look like B.E. Whites; some clubs in Europe have the cec mice as their B.E. White mice, though when they moult, they will have the beige watermarks denoting their genetics, which is common for the extreme dilute colors. There is no head spot to them and they are not genetically Siamese, just the lighter points make them look this way.

Regarding the Silver Black/Silver Grey mice, these mice are the silvered gene (si), not the Chinchilla gene. Silver Black is the dark version (looks black with silvering) and has no undercolor, Silver Grey is the medium version (looks gray with silvering) and has a light undercolor, of England’s Silver Gray mice (they used to recognize 3 shades—dark, medium, light—and dropped all but the dark shade at one point but recent standards show them back). We chose to standardize the dark version and the medium version as separate standards. The dark, medium, light is either referring to the amount of silvering, the amount of undercolor, or shade of the base color depending on what literature you read. When breeding a Silver Grey with a black-based PEW, you get Black, not Agouti which shows they are not Chinchilla mice. The Chinchilla version of Agouti is Chinchilla (with white belly from the Tan gene, otherwise it is known as Silver Agouti when it has no white belly). The Chinchilla version of Blue is called Squirrel.

Silver Black mouse
A Silver Black Standard mouse owned and bred by Karen Robbins. Photo ©2007 Karen Robbins.
Silver Grey mouse
A Silver Grey Standard mouse owned and bred by Karen Robbins. Photo ©2007 Karen Robbins.

Roan mouse
A Black Roan mouse owned by Kelli Boka, bred by Jennifer Hipsley. Photo ©2008 Karen Robbins.

Roan and Merle were developed by Jack Ball in San Jose, CA, back in the 1980s. We have two articles online you can read to learn more about them: Roan Mice and Explanation of Roan Mouse Inheritance Factors. The ones fanciers have is caused by a recessive gene but there is also a dominant one in the labs. Yes, it is random in what you get in the litters. Breeding two Merles will produce lots of Roan. The Merles also vary in the ratio of Roan to Merle from mostly Roan to mostly solid Merle patches. Also, the placement of the Merle patches can be one-sided like the mouse in the photo below, so these take a lot of work to get the ratio right along with the placement of the solid patches. You can get Roan and Merle in many different colors. These mice (along with Splashed and recessive red/yellow) were sent to Dr. Roland Fischer in Germany in 2009 (from Mike Chiodo in NY) and are now all over Europe.

Merle mouse right side
A Black Merle mouse right side, owned by Kelli Boka, bred by Jennifer Hipsley. Photo ©2008 Karen Robbins.
Merle mouse left side
. . . and the Black Merle mouse left side, owned by Kelli Boka, bred by Jennifer Hipsley. Photo ©2008 Karen Robbins.
Chocolate and Black Splashed mice
Chocolate Splashed and Black Classic Splashed mice, owned and bred by Karen Robbins. Photo ©2013 Karen Robbins.

The Splashed mice are an interesting color to work with and we have a couple articles on them: Splashed Mice and Transgenic Mice & Tricolors. They are the Transgenic lab mice (had gene splicing) and are a dominant gene. When combined with the spotted gene (ss) to add white, you can make what looks like a calico/tri-color with different colored patches all over, but instead of black, orange, and white you get Black, brown patches from Beige or Siamese, and white. They can be made in other color variations such as Blue, Lilac, Chocolate, Fawn, etc. These are not a true calico/tri-color gene but made to look similar. AFRMA calls this pattern BrokenMulti since you can make this affect many different ways and it could come in more than three colors on one mouse. *

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July 15, 2017