This article is from the May/June 1987 AFRMA Rat & Mouse Tales news-magazine.
By Jack L. Ball – Oct. 30, 1986
I am dating this material, as possibly my findings will be altered somewhat with the passage of more time and more generations of roan mice. I feel that, as one of the few people in this country engaged actively in the pursuit of the “roan” gene in mice, that I should put my findings down on paper for whoever may wish to read them.
The roan gene is elusive and not very easily understood by a novice like myself. I do not claim to have great knowledge of genetics. I am just a mouse breeder who likes to produce a different breed of mice than what is generally being produced by other breeders.
The roan gene in mice is listed as a lethal gene in most genetics texts. This, to me, means that if you breed two roans together, you will have a reduced litter due to the fact that many of the embryos or fetuses will die before birth and be absorbed, and possibly some others will not live long after being born. My past experience with breeding “lethals” of other types (mainly, black-eyed yellows) tells me the best way to successfully breed lethals, is to breed one lethal parent to another parent that has the lethal gene within its make-up, but does not show it outwardly. Lethals are usually a dominant gene and the ones that die before birth, or shortly after, are the product of two lethal genes combining (homozygous). So, what we want to produce is the “heterozygous,” or one that has one lethal gene and one non-lethal gene and shows the lethal coloration that we desire to produce. I suspect that the genetics of the case is more complicated than this explanation, but this is all I can figure out from my own experience with these and other lethal mice I have bred.
Since the roan gene involves only color, it is possible to get these mice in several coat types available such as “normal,” Satin, and Long-hair (or whatever other odd types are available). I suppose you could have “waltzing” mice of the roan coloration, also. As I say, roan refers only to color and all other genes would be on a separate scale from those containing the roan genetic material.
There seems to be several color varieties of roan mice. I guess the colors could be as endless as whatever colors are available in mice generally. Here again, the roan gene is separate from the color gene itself, since roan is a color pattern, not just one particular color. But, just for the record, I will list the most common colors I have found so far in the roan mice I have bred.
Besides the several color variations in the roan mice, I have found that there are also two distinct “types” in the roans. I will explain this further.
Type One: This is the type of roan mouse, where, as I describe it, the color and solid spot patterns are set and in place at the time the baby mouse first gets his full coat of hair. (You will understand this further when I explain “Type Two” later.) I notice on a Type One roan mouse, it is readily distinguished at an early age because there is a lot of white mixed in with the roan coloration right from the beginning. This animal does not change or lighten later. A Black Roan that is Type One looks like a Blue Tick Hound, so this may help you understand what I am trying to describe here.
Type Two: In this type, the young baby mouse with his first full coat of hair shows some mottling or variation in his coat color, even spots, but the difference between the solid spots and the roan is not highly distinct at the baby stage. As the young mouse gets older, usually by four or five weeks, the roan areas undergo a rapid fade out to a lighter roan color, making the solid spotted areas more distinct and attractive.
These are the basic and most obvious roan types and coloration I have seen in my own mice so far. The slight differences and shadings I have not sought to describe here, as the list could be endless.
As with other mice, these roans come in the “fox” type with the distinct light or white belly. Also, some come in the mottled or dark bellied (normal) type seen in most mice, just a continuation on the belly of whatever color or pattern was above. I have not yet bred a true tan-bellied roan mouse, although I have bred several chocolate roans that have a tan or orange fringe around the edge of the belly divider line. These are very attractive and I hope to breed more of these into the line as time goes by.
As one who has devoted more than a year of his life to pursuit of the tortoiseshell and roan gene, I can tell you that it is a fascinating and frustrating experience. Many of what I call “common” mice are produced as a by-product. But the more outstanding and beautiful individuals that are produced make it a worthwhile past-time for one who is willing to take his disappointments and keep on trying.