The Himalayan Variety

About the standards of different clubs: to my knowledge, most (if not all) American clubs do not recognize the Himalayan variety unless the rat has PINK eyes. In Europe, some clubs recognize both eye colors for Himalayan. (Himalayan rats with pink eyes, not ruby, occur when the rat carries one albino gene (chc) instead of two of the Himalayan gene, chch. I wrote an article on the genetics of the Siamese/Himalayan varieties which appeared in the November/December 1997 (Volume 3, Issue 4) of Rat & Mouse Gazette.

~Roxanne Fitzgerald

Have you ever seen a Himalayan rabbit or cavy? The main body color is white, while the "points" at nose, tail, ears, and feet contrast in a rich, dark brown, which sets off the paleness of the body color. In contrast, many Himalayan rats can only be distinguished from Pink-Eyed Whites by close scrutiny, which reveals a pale, milky-coffee brown smudge on the nose and at the tail base. Others have a little colored shading on the hands and feet. This delicate shading can be attractive, but it does not have the immediate visual impact for which the Himalayan color pattern is famous.

Over the years, breeders have worked hard to bring the Himalayan rat closer to the standard, which states that the points should be a "rich dark sepia (as dark as possible)." However, their efforts have often been limited by the assumption that Himalayan rats should have a certain genetic makeup. Nowadays, that assumption is in fast decline, and the Himalayan variety is (in my opinion) improving as a result.

Himalayan and Siamese color patterns are both caused by the Himalayan gene, ch, which acts at the albino locus. It works like the albino gene, c, by stopping production of color pigment, leaving the coat white. However, the Himalayan gene does not bleach out color all over like the albino gene. Instead, it allows color to be expressed only on the colder areas of the animal - the 'points' - while suppressing it on the warmer areas of the body. The Himalayan gene is incompletely dominant to the albino gene, which means that a rat which has one of each (in genetic shorthand, ch c) looks different from one which has two albino genes (c c) (a Pink-Eyed White) or two Himalayan genes (ch ch). The rat with two Himalayan genes has deeper coloring than the rat with just one. The best example of this is the show quality Siamese rat, whose deep, dark points and shaded beige body color are caused mainly by its two Himalayan genes ch ch. If you cross a Siamese rat with a Pink-Eyed White, the babies will have one gene from each parent at this locus, so they will have a ch from the Siamese, and a c from the Pink-Eyed White. Because of incomplete dominance, their color will be like a mixture of the two varieties; they will be pale Himalayans, with genes ch c at the albino locus.

Until recently, many people have assumed that Himalayan rats should be just like this; that they should have the genes ch c at the albino locus. These rats are heterozygotes, which simply means that they have two different genes governing the relevant attribute. A homozygote has two identical genes at this locus.

Apparently, the main reason that Himalayan rats are associated with ch c is because that was the usual basis for Himalayan coloring in the English mouse fancy at the time when the variety was established in rats. However, other fancies have different conventions. Himalayan rabbits and cavies are homozygous for the Himalayan gene. In Color Inheritance in Small Livestock by Roy Robinson (published by Fur & Feather in 1978), the Himalayan gene in the cavy is described as ca, but its effect is similar to ch. The genotype of the Himalayan cavy is given as ca ca, and that of the seal-point Himalayan rabbit as ch ch.

There is no reason why a Himalayan rat should not also be a homozygote, as long as it conforms to the Himalayan standard. The standard contains nothing that implies Himalayans should be genetically ch c rather than ch ch - show standards relate to what a rat looks like (its phenotype), rather than what genes it carries (its genotype). Of course, the genes are largely what make a rat look the way it does. However, other factors such as the environment, diet, and chance all affect its looks, too. For example, a rat which has lost a leg in an accident has the same genotype as its identical twin, but its phenotype is different. Conversely, there are rats which look similar, but have different genotypes. There are several different genetic combinations which produce Berkshire and Variegated rats, but the end product looks broadly the same. In the animal fancies, if it looks like a Himalayan, or a Berkshire, or a Variegated, it is a Himalayan, Berkshire, or Variegated. Fortunately, the rat fancy is free from the sort of animal apartheid which holds that only those with a certain "pure" genetic composition can be classified as a "true" example of its variety. This is practical as well as sensible, since DNA testing is not available at rat shows!

Himalayan rats which are ch ch have red eyes. The body color varies from white in the best specimens, to beige in the darker, Siamese-type rats. The darkest points are always found on these homozygotes, and with careful breeding, the shading can be lost from the body color, leaving just well-defined points. Rats which are ch c never develop points which are as dark and well-defined as those which are ch ch.

The difference between the Siamese and the homozygotic Himalayan are caused by polygenes - minor genes which subtly alter a feature, but which do not work with the mathematical precision of the major genes. This means that selective breeding for light body types will produce a rat which shares two Himalayan genes with its Siamese counterpart, but a different set of polygenes accounts for its paler shade. One way to tell the difference between the two types is to look closely at the eyes. Although both types of Himalayan will have red eyes, the homozygote has a very thin blue ring around the iris, as does the Siamese.

In my breeding program, I have selected for rats with the palest body color and well-defined points. The body color is usually a pale cream, but in the best animals it is white. The points are far darker than those seen on heterozygotic Himalayans. The eyes are red and I find that the rats with the palest eyes as kittens develop palest body color as adults. The males always develop some shading over the hindquarters, so I only show the females, as their body color is paler. In this respect, it is the opposite of showing Siamese, where normally only males are shown. I do not show animals with any shading over the hindquarters, as this is clearly not to standard, and I believe that it would be wasting the judge's time. In a similar vein, Nick Mays' history of the Himalayan rat (Pro-Rat-a 84) cautions against showing 'half and half' rats which are poorly shaded, fulfilling neither the Siamese nor Himalayan standards. For the same reason, I do not breed my Himalayans with show quality Siamese, because the result would be rats which were too dark to be good Himalayans, and too pale to be good Siamese.