The C-Locus

Introduction

The c-locus, technically known as Tyr^c (which shall be referred to as c from this point on) is responsible for many of the most fancy, and the most mundane, varieties of mice in the fancy mouse kingdom. There are several modifiers to this gene which have different effects on the pigment in the coats of mice. For some background into the different genes, the Jackson Laboratories web page is a fountain of information, if one knows where to look. For the undiluted article, please visit Jax at: http://www.informatics.jax.org/

Jax Information

In short, some of the points of interest of the above-mentioned article follow:

Albino is a very old mutation known in the Greek and Roman times. It originated in Asia and traveled throughout Europe and to the new world. Albinism is the result of a lack of melanin pigments. Albino mutation affects the amount of tyrosinase, and thus of melanin, in pigment cells, but does not interfere with the production of pigment cells themselves. All of the modifiers to the basic albino gene, c are recessive to the wild type in appearance, but mice which are heterozygous with wild type often produce intermediate amounts of tyrosinase. Therefore there can be some dilution of coat color even when a mouse is only heterozygous albino.

One of the problems that albino mice have is that homozygotes do not perform as well as normal in a number of behavioral tests. This problem is caused by the lack of pigment cells in the eye, which aid in vision.

C-locus modifiers

Acromelanic c^a

c^a is fully recessive to wild type and completely dominant to c. Homozygotes are distinguishable from albino at birth by pigmented eyes. Both young and adult c^a homozygotes have an off-white coat color, pigmented eyes, ears, tail, and anal region. Unlike Siamese homozygotes, no dark hairs appear on the nose. With respect to coat color, acromelanic is between chinchilla and extreme dilution in the albino series of phenotypes.

c/c^a heterozygotes have a slightly off-white coat color, dark eyes, and slightly sooty ears and tail.

c^a/c^ch heterozygotes have a coat color intermediate between chinchilla and acromelanic homozygotes, with a very darkly pigmented anal region.

c^a/c^e heterozygotes have a lighter coat but darker ears and tail than extreme dilution homozygotes and are indistinguishable from acromelanic homozygotes. In combination with c^h, the coat is lighter and again indistinguishable from acromelanic homozygotes, but the eyes are pigmented in addition to the dark ears and tail

Chinchilla c^ch

Agouti chinchilla mice are gray rather than brownish gray. The yellow pigment in the hair is greatly reduced and the black pigment slightly so. Eyes are black. Tyrosinase activity in the skin is about one-third that of normal. Heterozygotes with c^h, c^e, and c are intermediate in color.

Extreme dilution c^e

This mutation was found in the wild. The hair is very light gray, and eyes are black. c^e/c mice are almost white with black eyes.

Himalayan c^h

In homozygotes, the first coat is a uniform light tan. At the first molt, the body hair becomes lighter and the ears, nose, tail, and scrotum become dark as in Siamese cats. Body hair may be very light or quite sooty, depending on the genetic background. Eyes are slightly pigmented and appear red. c^h/c and c^h/c^e mice are intermediate between the homozygotes, Pigment synthesis in Himalayan mice is temperature-sensitive; pigment develops in growing hairs of mice housed at 15ºC but not in those housed at 30ºC.

Platinum c^p

Homozygotes are lighter than extreme dilution homozygotes and have pink eyes. c^p/c mice are intermediate between platinum and albino homozygotes

Ruby-Eyed Dilute c^r

This albino series mutation was found in a nonagouti chinchilla (a/a c^ch/c^ch) stock at Harwell. Homozygotes have reduced black pigment and no yellow pigment. They are lighter than homozygous chinchilla but darker than homozygous extreme dilution mice. Eyes are ruby in adults. Heterozygotes with other albino locus mutations are intermediate.

Finnmouse Information

On the Finnmouse site there is a great deal of information regarding the combinations of alleles at the C-locus. I am not going to bother to re-create what has been so eloquently presented there. Please visit that site for the full details presented there. This article will focus only on a few combinations which are not discussed in detail on that site. Specifically the combination of the Chinchilla gene and the albino gene.

The Chinchilla-Albino Connection

The Chinchilla gene is useful in creating, among other things, the following varities: fox, chinchilla, BEW, silver agouti, and marten sable. A single chinchilla gene, combined with the Himalayan gene, is known to produce the Burmese pattern in mice. According to sources, a double chinchilla is necessary to producing all but the Burmese varieties.

It is my belief that the varieties mentioned above, or mice that look similar to them, can be obtained by a single chinchilla gene, if the gene is combined with an albino gene.

Now let’s discuss the founder albino/chinchilla mouse in my collection. Onion was purchased on December 22, 2001.

Onion

His genes, to the best of my understanding, are:

A/a B/* c^ch/c D/* P/P W^sh/w

While the Finnmouse site doesn’t elaborate on the combination of c^ch/c, Onion has been a great test case to demonstrate what colors are possible to obtain with an albino gene combined with a chinchilla gene.

Silver Agouti

Onion himself has the appearance of a silver agouti mouse The tips of his hairs are a bleached white color. Some websites declare that silver agouti mice have black tips to the strands of hairs, and others insist the tips resort to a pearl gray. Onion demonstrates the latter of these two assertions. The fact that he and Mavra have had albino offspring proves that he cannot have a double chinchilla gene, therefore demonstrating that a single chinchilla gene is often enough for the “chinchilla effect.” Since the chinchilla gene is recessive, yet dominant over the albino gene c, this makes sense. It makes sense that Onion should be a true silver agouti mouse, since his dominant c-allele determines the coloration. Some call him a “mock silver agouti” and that is fine.

Black-Eyed White

When bred to a fawn mouse with an albino recessive gene, some of the offspring were black-eyed white. Again sources say that a chinchillated fawn mouse, that is a fawn mouse with a double dose of the chinchilla gene, will be a black eyed white mouse. That a black eyed white was obtained without the need for a double dose of chinchilla is evidence once again that only a single chinchilla gene is necessary, if paired with an albino gene.

Chinchilla

Another offspring that Onion had was a chinchilla mouse. Silver agouti with a fox white belly. As with all other varieties mentioned, this is a coloration that is supposed to only happen when a mouse has a dual set of this gene.

Fox

Since a chinchilla mouse is a fox mouse, I would have to say that the combination of chinchilla and albino will probably result in a mouse with a white tummy if it has the a^t gene.

Future Possibilities

Using an albino/chinchilla combination, it is my plan to see if there is a difference between c^ch/c^ch brindle mice, and c^ch/c brindles. Also my BEW line of mice will incorporate the chinchilla gene so as to further dilute any hints of the color yellow that might spring up in the mice.

While a double dose of the chinchilla gene might result in more beautiful to-standards mice, the effects of chinchilla and albino is frequently indistinguishable from that of pure chinchilla. Only test matings to determine that the chinchilla-appearing mouse has an albino gene will determine the difference. When a fancy variety of mouse is desired, and only a heterozygous chinchilla mouse and albino are available, it is not impossible to achieve the desired look.