A list of currently known genes affecting markings in fancy rats, with chart showing the results of various combinations of genes.

  All colours of rats may be combined with the following markings:

Silver, which is a scattering of white guard hairs on the back, especially around the shoulders. All or nearly all Norway rats have some silvering: there is no known single gene which controls the degree of silvering, but some strains of rats are much more heavily silvered than others. For historical reasons black rats with silvering are called silver greys, and all fawns are called silver fawns whether they have visible silvering or not. Silvering shows up best on dark colours, and is most marked in young adult bucks.

Husky, producing a scattering of white hairs so intense that they make up a significant proportion of the coat and change the apparent colour, so that e.g. black huskies look charcoal-grey. Husky rats are born with plain, un-roaned coats, and the silvering appears almost overnight at around seven weeks. They always or nearly always have a white belly and muzzle and a blaze - often a broad, triangular badger-face blaze with the point extending almost to the crown of the skull. The eyes have a ruby retina and a blue-tinged iris.

As they age they turn white from the nose back, until the entire face is white and the blaze is lost. White also spreads from the belly up the sides. In young animals the white belly may have uneven, wandering edges, but as it spreads it straightens out and takes in the limbs and throat as well. A middle-aged husky rat looks as if someone took a plain white animal and then painted a perfectly straight two-inch wide coloured stripe from the crown of its head to its tail.

The hood series, in which the distribution of the melanocytes which produce skin pigmentation is restricted to varying degrees in the embryo. These melanocytes spread from the central nervous system to the rest of the body: the marked patterns progressively withdraw colour from the body back towards the spine and skull.

The genetics of the hood series are complex and involve combinations of several co-dominant genes: e.g. breeding hooded to self produces Berkshires. Nor are these markings purely controlled by genes. Masked, black-eyed white and odd-eyed-white rats are all homozygous for the Extreme Hooded gene, which restricts colour to the front of the skull: but it seems to be mainly chance and developmental factors which decide whether the animal will have colour only in the eyes or right across the face.

The stages of the hood series are as follows:

Self?????????????, i.e. without any white markings

Self with white on the hands and feet - considered a fault for show purposes

Irish - solid coloured with a small area of white on the underside and white on the hands and feet. An ideal show-quality Irish has white on the fingers and toes, extending to the wrists at the front and halfway up the soles of the feet at the back; a large white triangle (point down) on the chest; a white (i.e. pink) tail-tip and a white star on the forehead. The last is rarely seen.

Berkshire - solid-coloured with a white belly, hands and feet. A show-quality Berkshire should have white over the entire belly, with neat straight edges along the flanks; a head-spot or blaze; white feet to the ankle and white hands to halfway up the forearms; and the tail divided about half and half, the end portion being white (i.e. pink). In practice most British Berkshires either have large irregular white blobs on the stomach or an all-white stomach with white streaks trailing up the flanks, and a head-spot is rarely seen. American Berkshires are slightly different genetically, and are more likely to have a head-spot and a neat-edged white belly, like that of a fox-marked mouse.

Blazed Berkshires have a wide triangular blaze like that of a young husky rat.

Chinchilla - with a white belly as for Berskshire but with all red pigment eliminated from the coat, leaving a silvery, irridescent pale grey - basically white fur with black ticking. This marking is dominant, and always heterozygous: the double gene is lethal.

These animals are born as normal red-brown agoutis and then lose the red as they age. This gene is probably related to the guinea-pig colour Fading Yellow - and should probably be described as Progressive Chinchilla, just in case the more common rodent chinchillation gene (which is on the Colour locus, and is effective from birth) ever shows up in Norway rats.

Essex (formerly known as Robert) markings - as for Berkshire but with evenly distributed white freckles on the sides and preferably on the back.

Roan - similar to the Essex, but producing sterile males. This gene was described decades ago and is not now known - unless in fact it was the Essex with a linked gene which was causing the sterility problem and which has since been detached.

Variegation: a coloured head and shoulders; white belly; preferably a white head-spot; coloured freckles on a white ground on the back and sides; and a freckled or parti-coloured tail. There is often a coloured stripe down the back as well, though this is a fault for show purposes.

Blazed Variegated rats have a wide triangular blaze like that of a young husky rat.

Hood: coloured head and shoulders and a stripe down the back. Ideally the stripe should be straight and narrow with clean straight edges, extending from the shoulders to the root of the tail, and although there will nearly always be a white tail-tip as much of the tail should be coloured as possible.

Bareback: coloured head and shoulders and the rest of the body white.

Cap: coloured head, with a white lower jaw and throat, and preferably a small white blaze or a head-spot.

Mask: colour on the upper surface of the muzzle and around the eyes only.

Black-eyed white: colour restricted to the eyes only - though in fact most animals also have smudges of colour behind the ears and/or round the eyelids.

Odd-eyed white: one black and one pink eye, usually with a small patch of coloured coat around the black eye.

In variegated, hooded and bareback animals the colour on the shoulders may or may not also extend down the forelegs to the wrist, though for show purposes the forelegs should be white. Many of these animals have odd spots of colour on the sides or belly which are considered a fault for showing. In particular, bucks often have round coloured dots over the ureters, to either side of and about half an inch in front of the penis (this area of skin is very thin and sometimes ulcerates in very old males).

Hooded animals often have a very irregular stripe, and/or blotches on their sides. In extreme cases you can get an animal with large coloured patches, resembling the pattern which in other animals is variously called broken, piebald/skewbald or paint. However there are no known true broken-marked fancy rats at present. A combination of the hood and chinchilla genes does produce true broken-marked or patched rats, but the combination is semi-lethal: most of these animals have malformed guts and die very young.

Chinchilla is currently regarded as part of the Hood or White Spotting series, but I personally find it very hard to believe that chinchillation really is part of the hooded sequence, since it does something entirely different. All other genes on the H locus modify the distribution-pattern of melanocytes in the skin, whereas in chinchillas the melanocytes are evenly distributed but lose their ability to produce red pigment (phaeomelanin).

In some black capped and black masked rats - hhe and hehe - the Extreme Hooded gene he produces a slight chinchillation effect, so that the markings come out a greyish chocolate colour. But some capped and masked rats have fully black markings. This indicates that the fading effect is not due to the he gene per se but to an unidentified linked gene. I suspect chinchillation is a Hood-series gene producing a white belly, initimately linked with another allele of the gene which causes faded colour in capped rats.






Hooded or White-Spotted














extreme hooded

restriction of colour to the face



body-colour withdrawn towards spine

Hood Modifier



full extension of coloured markings towards tail



coloured markings withdrawn towards head




wild-type unroaned coat



Progressive roaning, as seen in husky rats.


Colour Ê

Locus ð


Hood Modifier

Self: coloured body without white markings, or with markings restricted to fingers and toes



Irish: coloured body, with white markings on chest, hands and feet, tail-tip and possibly star



British Berskshire: coloured body with white belly, hands and feet, distal half of tail, sometimes with head-spot or blaze: edges of belly-marking usually irregular



American Berkshire: as British Berkshire but with straight-edged belly marking, and more likely to have a head-spot or blaze



Blazed Bershire: as for standard British or American Berkshire but with broad triangular white blaze covering face



Chinchilla: white belly, and red pigment progressively lost from coat to give irridescent silvery-grey appearance



Essex: coloured body with white markings as for Berkshire but with white freckles on sides



Roan: similar to Essex but males sterile



Variegated: white body with coloured head (sometimes with white head-spot) and shoulders, coloured freckles on back and sides and a parti-coloured tail



Blazed Variegated: as for standard Variegated but with broad triangular white blaze covering face



Hooded: white body with coloured head and shoulders and stripe (often patchy and broken) extending along spine and down the tail



Bareback: white body with coloured head and shoulders



Capped: white body with colour on and skull, variably arranged



Masked, Black-Eyed White and Odd-Eyed White: white body with colour on frontal area of face only, variably arranged