Coat types

Body types


Pink eye dilute

Pink eye dilute is a very common colour in the UK, and is one of the colours that has been around since even before the fancy. Alleles at this locus are:

  • P – Dominant wild type (so “no effect”). Normal pigment.
  • p – Recessive pink eye dilute gene. Black pigment is reduced to a pale cream, yellow pigment remains basically unchanged. Eyes are pale pink.

A-pp: silver fawn

A-pp: silver fawn

aapp: champagne

aapp: champagne

Minks and pearls

Mink rats seemed fairly uncomplicated until around 2000, when mink rats were imported to the UK from American lines. When these newcomers were mated with the existing minks, it became apparent we had two completely separate but similar looking genes in play. These are generally known as mink (or English mink), and American mink (or mock mink).

The pearl gene appears to create a longer pale/white undercoat, pushing the pigment closer to the tips of the fur. This gene only has an effect on mink based rats (of either type).

Mink is at the m (mink) locus. The alleles of this locus are:

  • M – Dominant wild type (so “no effect”), the rat has normal pigment.
  • m – Recessive mink. The black pigment is diluted to a brown or grey colour, sometimes with a slight white or pale undercoat. Yellow pigment is slightly diluted.

American mink has not been officially allocated a symbol, but for use in the fancy I use the am (American mink) locus. The alleles here are:

  • Am – Dominant wild type (so “no effect”), the rat has normal pigment.
  • am – Recessive American mink. The black pigment is diluted to a brown colour. Yellow pigment is slightly duller.

Pearl is at the Pe (pearl) locus. The alleles of this locus are:

  • pe – Recessive wild type (so “no effect”), the rat has normal pigment.
  • Pe – Lethal dominant pearl gene. A rat inheriting two copies of this allele will never be born. Mink based rats with one copy of this gene will have a longer pale undercoat, with more pigmentation nearer the tips of the fur.

The phrase “lethal dominant” can be worrisome, but all it means is that rats with two copies of the pearl allele are not viable, and so never born. It does not mean that there is anything wrong with pearl rats, and no issue with kittens suffering.

aamm or aaamam: mink

aamm or aaamam: mink

A-mm: cinnamon

A-mm: cinnamon

A-amam: cinnamon

A-amam: cinnamon

aammPepe or aaamamPepe: Pearl

aammPepe or aaamamPepe: Pearl

A-mmPepe or A-amamPepe: cinnamon pearl

A-mmPepe or A-amamPepe: cinnamon pearl


There are two different blue genes in the fancy – British blue and Russian blue. Both are entirely separate genes, with the only similarity between the two being that they give a grey colouring that’s been named blue.

British blue is at the D (dilute) locus. The alleles at this locus are:

  • D – Dominant wild type (so “no effect”), the rat has normal dense pigment.
  • d – Recessive dilute blue. The black pigment is diluted to an even mid grey-blue. Yellow pigment is diluted to a soft fawn colour.

Russian blue is at the Rb (Russian blue) locus. The alleles at this locus are:

  • Rb – Dominant wild type (so “no effect”). The rat has normal dense pigment and a normal coat.
  • rb – Recessive Russian blue dilute gene. The black pigment is diluted to a deep steel grey, and the yellow pigment is reduced to fawn. In this case, the pigment doesn’t dilute evenly, resulting in clumps of pigment on the hair shaft – this gives a speckled effect to the colour called heathering. This gene also affects the fur, giving a somewhat shorter and denser coat than average in rats without the Russian gene.

Confusingly, different symbols are used for these genes in different countries, but in the UK the notation used is pretty fixed. In the US, British blue (which is known as slate blue, American blue, or just blue) is given the symbol “g” (for grey), and Russian blue is assigned the “d” notation.

Occasionally breeders across the world talk about other varieties. In Europe there have been claims of a third shade called German Blue, in America a new gene has been called Midnight Blue, and “Leaden” has been talked about in the past. While these varieties may well exist genetically they have not been widely bred or standardised in the fancy.

aaD-Rb-: Black

aaddRb-: British blue

aaD-rbrb: Russian blue

aaddrbrb: Russian silver

A-ddRb-: British blue agouti

A-D-rbrb: Russian blue agouti



Black eyed

Burmese & black eyed

These genes only show their effects on rats who already have a combination of the albino, Himalayan, and/or marten alleles on the c locus. Although the black eyed gene has been scientifically described, the Burmese gene hasn’t as of yet. The idea that these two genes are allelic is a fairly new idea, but it is backed by breeding results and explains many slightly odd breeding results over the years. The alleles at this locus are:

  • be – Recessive wild type (so “no effect”, c-locus rats have the appropriate colouring to their c-locus genetics).
  • BeBu – Burmese. Dominant to both other alleles. Overall body colour is darkened to a seal brown colour, yellow pigment is dulled, and eyes are black.
  • Be – Black eye. Dominant to wild type, recessive to Burmese. Eyes in all c-locus varieties are black, and the overall coat colour is slightly warmer/creamier.

With some of these varieties, it doesn’t matter if they are agouti or non-agouti based, they remain the same variety – for these, I have not included the A locus in the genotype below the photo, and you can assume that both A- or aa would give rats that look the same.

aa BeBuBeBu chch: Sable Burmese

aa BeBu- chch: Burmese

A- BeBu- chch: Wheaten Burmese

Be- chch: Black eyed Siamese

Be- cch: Black eyed Himalayan

Be- cc: Ivory

C locus

Known as the Colour locus, hence the symbol C. This is also sometimes referred to as the albino locus. Alleles at this locus are:

  • C – Dominant wild type (so “no effect”)
  • ch – Himalayan, an acromelanistic pattern – pigment only appears depending on the temperature, so the cooler parts of the animal are coloured. In rats this is the face, ears, tail, and feet. Eyes are red to ruby.
  • cm – Marten. Yellow pigment is almost entirely removed and becomes silver or very pale yellow. Black pigment is normal in babies, and a charcoal grey in adults. Eyes are pink to red.
  • c – Albino. No pigment is expressed at all, so fur remains entirely white, and eyes are bright pink.

The wild type allele is dominant to all others here, but the other three alleles are all codominant. With Siamese, Himalayan, and albino, it doesn’t matter if the rat is agouti or non-agouti based (A- or aa), the look of the rat will be the same – for these varieties it is not important whether the rat is agouti based or not.

aaCC, aaCc, aaCch, or aaCcm: Full colour black.

chch: Siamese

chc: Himalayan

cc: Albino

aacmcm: Marten


Officially known as brown (hence it being the B locus), we tend to call the effects of this gene chocolate in rats. It’s a fairly old gene, first being described by Castle and King in 1932. The alleles at this locus are:

  • B – Dominant wild type (so “no effect”)
  • b – Recessive brown gene. Black pigment becomes deep chocolate brown. Yellow pigment is not changed.

In other fancies both light and dark brown mutations have been recorded here, so maybe we have more shades of brown to look forward to in future.


aaB-: Black

aabb: Chocolate

A-bb: Chocolate agouti


The agouti gene is one which most fanciers will recognise the effects of, and usually it’s very clear and easy to spot the effects of this gene. The alleles at this locus are:

  • A– agouti, wild type. The fur on the back and sides is grey at the roots, then there is a band of yellow, then black tips (this is often referred to as ticking). On the belly there is less black pigment and almost no yellow pigment, so the belly looks silvery grey.
  • a – non-agouti. The fur lacks the yellow banding, so it is the same colour from root to tip. The belly is no longer paler, so the rat is the same colour all over.

A variety has been bred in the US which is theorised to be melanistic agouti (am), but this hasn’t been imported into the UK yet.


A-: Agouti

aa: Non-agouti

Cap stripe

Not a standardised variety in the UK, but cap-stripes have been exhibited in some US rat clubs, though they’re not currently recognised for showing. There are no plans to recognise them in the UK or anyone breeding them for show, as far as I am aware.

There are two distinct types of cap-stripes. The first is to do with the chinchilla white spotting gene, and is a combination of that with markings on the H locus. This combination can be prone to megacolon in some lines, especially in the US. The other is a combination of the UK roan gene again with H-locus marking genes, which can give a cap-stripe effect – this marking will roan out as the rat grows.