Some of the rats in my lines carry what breeders call the C-locus gene. This gene affects how pigment is distributed across the coat and can create animals with lighter bodies and darker points on the face, feet, and tail.

A classic example of a C-locus trait is the Himalayan variety. These rats often have very light or white bodies with darker coloured points, typically on the face, ears, feet, and tail. The exact point colour can vary depending on the base colour genetics, and the contrast between body and points can be subtle or strong depending on how the specific genes interact. Researchers use the term acromelanism to describe this effect where pigmentation is temperature dependent. Because the extremities of the body are cooler, pigment develops more strongly there than on the warmer torso.

Some breeders refer to other C-locus based patterns like Siamese or Burmese, but the Himalayan pattern remains one of the most recognizable due to its contrast and classic style.

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Another fascinating trait I see is Tonkinese colouring. Tonkinese is also a product of the C-locus gene but interacts differently than Himalayan and Siamese. When the specific Tonkinese allele is present, the result can be a coat that has gentle pointing but not as stark a contrast as Himalayan or Siamese. Depending on the genetic combination, the effect can range from a warm, even colour with subtle darker extremities to richer point contrast that still blends into the body colour.

Tonkinese genetics are unique because the effect on the coat is visible even with just one copy of the Tonkinese gene. That means a wide variety of expression is possible, and the depth of the point colour can vary across individuals in a litter.

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The Red Eye Dilute gene is a recessive modifier that affects both coat shade and eye color. When a rat carries two copies of this gene, the eyes become red or ruby rather than the typical dark colour, and the coat becomes lighter overall. This gene doesn’t alter the underlying colour pattern as much as it softens and lightens the entire look of the animal.

In many breeding lines this modifier creates gentle warm tones and can make colours appear creamier or more muted than their standard counterparts. It’s a lovely trait when combined with other colour modifiers because it produces subtle shades that are very pleasant to look at.

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Pearl is another dilute modifier, but it only shows up on rats that already carry a specific base colour (often related to the mink family of colours). On a Mink background, Pearl will lighten the coat and often give it a soft silvery cast. On other backgrounds it might blend with the base colour to create interesting visual effects with cream, silver, or pale tones.

Because Pearl interacts with other genes, it can create variations that are soft and subtle, and sometimes it can be hard to identify without knowing the genetic background of the parents.

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When rats carry two copies of the blue dilution gene, the usual coat colour is dulled into a slate or steel version of itself. This is often simply called “Blue” in fancy rat terms, and it can appear in both solid and patterned rats. Blue is a recessive trait, so a rat must receive a blue gene from both parents for the colour to show.

Visually, blue coats are a lovely soft grey-blue shade that can vary in intensity depending on other modifiers or the underlying colour genetics. In some backgrounds, blue can appear warmer or cooler, but the unifying theme is always that softened, smoky look.

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Some of the most interesting and less formally defined traits in my lines are things like shadow, mottled, or tortoiseshell types. These traits don’t yet have widely agreed show standards, but many breeders describe them as complex, mixed colour effects where the coat shows a blend or patchwork of colours that can resemble fine shading or splash-type marks.

“Shadow” is sometimes used to describe a rat with a darker top colour and a paler belly or underside, but the exact genetics behind it aren’t yet fully understood in the community. Some breeders also associate shadow markings with tortoiseshell-like patterns, where pigment distribution creates varied and rich patches that differ from simple markings.

Because these traits are still being explored by breeders, you may see variation from one line to another, and part of the fun of working with them is watching how the colours express in each generation.

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