In making this page, I tried to simplify everything in an effort to make it easier for the new fancier. There is always room to learn more, a lot more. Genetics is an ever evolving field. This section will hopefully give you a great jump start in understanding the colors and markings of mice. To fully understand this section you must have a basic understanding of genetic Terms.
Understanding mouse genetics isn't about simply knowing what genotype produces a certain phenotype, such as; at/a* p/p is Lilac Tan. Truly understanding mouse genetics entails knowing why and how a genotype produces a specific phenotype. Once you have a basic understanding of this, genetics and breeding will become much easier to interpret. Within reason, you will be able to figure out genotypes that you have never seen before simply by applying what you know about how colors work.
Essentially there are only 2 colors that make the coat colors you see on mice. These 2 colors are Black (eumelanin) and Yellow (phaeomelanin). It is the distribution of these colors on each hair that give us what we see. For instance, blue (genetically dilute d/d) is simply black hairs which have uneven color distribution in each individual hair that makes the black pigment look lighter (gray).Think of it like a mosaic painting. When zoomed in you can see these individual colors and the specific vectors that colors are on the canvas, much like you can see (with a powerful lens) how and where the color(s) in each hair is distributed. However, when looking at the hair as a whole, like standing back from a mosaic painting, it looks much different. In the point at hand, uneven distribution of black pigment produces a gray (blue) appearance.
Different genes have different effects on Yellow and Black hairs, some dramatically, some minimally. A great way to illustrate the difference is to use a Black and Tan at/a* mouse as an example (shown to the upper left). Also for the sake of example, I will use Pink Eye Dilute p/p and Chinchilla Dilute cch/cch to illustrate how they each affect Black and Yellow hairs. I choose these 2 as examples because they have drastically different affects on Yellow and Black hairs.
Pink Eye Dilute p/p is on the P locus on chromosome 7. This dilute not only affects eye color but it also affects coat color. Pink Eye Dilute affects Black pigment drastically, while it has minimal affect on Yellow. When homozygous for Pink Eye Dilute, a Black Tan mouse will be diluted to a Lilac Tan at/a* p/p, shown here on the right. As you can see, the Pink Eye Dilute has diluted the black hairs of the mouse dramatically while leaving the yellow hairs nearly untouched.
Chinchilla Dilute cch/cch is on the C locus (also called the Albino Locus) and is on chromosome 7. Chinchilla Dilute greatly affects yellow pigment and minimally affects black pigment. When homozygous for Chinchilla Dilute, a Black Tan will will be diluted to a Black Fox at/a* cch/cch. As you can see in the picture on the left, the yellow belly is completely wiped of color, giving a snow white appearance. The black hairs remain quite dark (nearly black).
It is important to note that there are many different alleles found on the c-locus (chromosome 7) that we have in the fancy. Most of these other alleles have a stronger effect on both black and yellow than the Chinchilla Dilute, yet the principles are the same. They all have a stronger effect on Yellow pigment than Black. Look forward to a future C-dilute genetics section which will illustrate this. Also look forward to the Agouti Locus which will explain more on color distribution.