Coat types

Body types


Lavender Agouti

Another variety that is not shown in the UK as it is too similar to other existing varieties, so the lack of selection means that this combination can be quite variable. Generally it will vary from looking like a slightly washed out Blue Agouti, to something resembling a Lilac Agouti but with a distinct blue tone rather than the required pink.

Genetics: Agouti with two copies of the English Mink gene and two copies of the blue gene (A-ddmm).


This is not a standardised variety in the UK, as it is not considered distinct enough from other existing varieties. A combination of Blue and Mink, the shade produced is very variable but in general resembles a Lilac with a distinct blue tinge.

Genetics: Non-Agouti with two copies of the English Mink gene and two copies of the Blue gene (aaddmm).

American Blue

AKA: Sky blue

Sky Blue

The Blue gene can give a whole range of colours, from a pale, powdery blue over a white undercoat to a deep, rich slate down to the skin. The UK standard asks for a deep steel blue, and that dark shade we refer to as “British Blue“.

Although the US standard also refers to the same deep steel blue, in the UK we use the term “American Blue” to refer to a paler blue, what is also referred to as “Sky Blue” in the US.

There is also (understandably) confusion between American/Sky Blue and Powder Blue, but powder is a more muted shade overall, and has a pale base coat.

Genetics: Non-Agouti with the dilute gene (aadd), selected for bright and clear colour.

AFRMA (proposed) Standard: Color to be in-between Blue and Powder Blue—a clear sparkling blue color showing no brown patches or silvering. Eye color to be dark ruby or black.


AKA topaz

Silver Agouti

The Silver Agouti is the Agouti form of the Marten, and was first bred in the UK in September 2010. The name is taken from silver agouti mice, which these rats resemble.

Genetics: A-cmcm (Agouti, with two copies of the Marten allele at the c-locus), or A-cmc (Agouti, with one copy of the Marten allele and one of the Albino allele at the c-locus). Black Eyed Silver Agoutis must also have at least one copy of the black eye gene (so A-Be-cmcm or A-Be-cmc)

NFRS Standard: Body colour mid grey with light heathering, with no suggestion of brown or blue tones. Fur on the face to be lighter on the whisker bed, over the eyes and behind the ears. Belly colour a slightly paler shade of grey than the top. Foot colour to match top. Eyes pink or black. Faults: rusty patches, white toes or patches, darker points on the nose, tail root or feet.


The roan gene, also known as husky or European husky, is responsible for the vast majority of worried “why has my rat changed colour?” threads (the remainder being the work of Siamese kittens moulting into their adult coat). This gene has not been scientifically described, but commonly it is given the ro (roan) symbol. The alleles at this locus are:

  • Ro – dominant wild type allele, so “no effect”.
  • ro – recessive roan allele. The rat has white markings on the stomach and face. From the first moult onwards the fur roans to white, gradually becoming more and more roaned until the rat is almost solid white.

The amount of white spotting on a roan is also dependent on the H locus genes involved. A self, Irish, or low white Berkshire with the roan gene would tend to be a roan (or “full roan”). A hooded or variegated type may end up being closer to a striped roan. A capped or similarly marked rat would likely end up being closer to a cap-stripe roan.


The rat variety called chinchilla is genetically very unlike chinchilla in the mouse. In the mouse the chinchilla colouration is caused by a c-locus mutation, and the white belly either by separate spotting genes or a-locus mutations. In rats, the chinchilla situation is more complicated. The main part of the story is a spotting gene given the locus Cs, for chinchilla spotting:

  • cs – recessive wild type gene, no white spotting.
  • Cs – dominant white spotting gene, the rat has a white underside and often white facial markings (a blaze or headspot). The gene tends to reduce yellow pigment slightly.

The white spotting gene has variously been referred to as husky, American husky, Aurora spotting, dominant blazed, or the high white gene. In the UK we tend to refer to it as chinchilla white spotting, as the gene tends to only be found in chinchilla lines.

In order to make the chinchilla variety, the rat must also have a second gene alongside the white spotting. This second gene is given the locus name of fy, for fading yellow. Alleles at this locus are:

  • Fy – incomplete dominant fading yellow gene. The black pigment is normal but the yellow pigment is reduced to pale yellow or white.
  • fy – wild type non-fading yellow gene. Yellow pigment is unaffected.

H locus and friends

Most rat markings are created by mutations at the H-locus. The most distinctive is probably the hooded, but the full variety is quite amazing. Opinions on which alleles actually exist in the fancy at the moment differ, but some known alleles include:

  • H – Wild type, minimum white spotting.
  • He – Quite extensive white spotting
  • hi – Irish, small amount of spotting confined to the underside
  • h – Hooded, extensive white spotting confined to the rear end of the animal
  • Hre – Restricted, extensive white spotting, lethal when homozygous
  • Hn – Notched, quite extensive white spotting
  • Hro – Robert type, lethal when homozygous, gives a small amount of white spotting with a fading effect

All of these mutations are co-dominant, meaning heterozygous rats are different varieties from homozygous rats.

There are several other loci which also modify the markings. First of all there’s the downunder locus. This is not scientifically described, but it’s sometimes given the symbol “Du”. The problem is that is already more commonly used for the dumbo locus, so I have chosen to use the following notation:

  • hdu – recessive wild type allele, so “no effect”.
  • Hdu – dominant downunder allele. The rat has pigment on the underside in a stripe down the centre. This may be broken up or patched depending on the effect of other h-locus alleles present.

Another important one is named the hooded modifier locus, and this controls the length of the stripe in hooded rats – as well as, presumably, having an effect on the amount of pigmentation visible in other non-hooded marked rats:

  • Hml – long dorsal hooded pattern. Necessary for hooded rats to have a stripe reaching right down to the tail.
  • Hms – short dorsal hooded pattern. Necessary for barebacks (of some genetic types) to have a short or non-existent saddle pattern.

The other really important thing to remember with markings is that we categorise them on what we see. A rat with two copies of the Irish allele might look like an Irish – or it might look like a Berkshire. A rat with one copy of the Irish allele might look like an Irish, but equally it could be a self with a couple of white toes. A rat with the Robert type gene is an Essex, but if there’s no selection for shading then it could look like a perfectly standard Berkshire. For these reasons, there will always be confusion and odd breeding results when dealing with marked varieties, and there will always be arguments and confusion over what particular marked variety a rat actually is.

Red eye dilute

The red eye dilute gene came over to the UK in the mid/late 80s, both from European imports and American imports. Although the gene is called red eye dilute, the eyes can often be dark enough to be mistaken for black. Alleles at this locus are:

  • R – Dominant wild type (so “no effect”). Normal pigment.
  • r – Recessive red eye dilute gene. Black pigment is reduced to a mid beige, yellow pigment is bright gold, eyes are red to dark ruby.

There is often some confusion due to names – the UK varieties of topaz and buff are called fawn and beige in America.

A-rr: topaz

A-rr: topaz

Buff, photo copyright Halcyon

aarr: buff