Colour genes

COLOUR GENES OF RATTUS NORVEGICUS
A list of currently known genes affecting coat and eye colour in fancy rats, with chart showing the results of various combinations of genes.

LOCI AND GENES AFFECTING COLOUR:

Locus

Code

Name

Description

Agouti

A

agouti

wild-type ticked and banded coat

a

self

extends colour of ticking to entire hair, giving a plain unticked, unbanded coat

Black

B

black

normal colouration of black elements of coat

b

brown

dilution of black elements of coat to brown

Colour

C

full colour

both black and yellow pigments (eumelanin and phaeomelanin) present

c^e

extreme dilution

normally black band of agouti coat - or whole hair in self coat - bleached to off-white; skin pale except on ears, tail and genitals, but black freckle appearing on tip of testicles, and very dark eyes: co-dominant with c^h

c^h

Himalayan

black pigmentation temperature-sensitive, only developing in on cold areas of body, plus partial chichillation (reduction in red pigment): co-dominant with c^e

c

albinism

complete absence of pigmentation

Dilute

D

dense colour

normal intensity of colour

d

dilute colour

lightening of colour, turning black elements of coat light steel-blue - this is due to eumelanin (black pigment) forming clumps instead of being evenly spread, so in fact dd animals have more eumelanin by weight than DD, and Dd animals can be slightly darker than DD

Grey

G

non-grey

normal intensity of colour

g

grey

lightening of colour, turning black elements of coat flat grey

Pink

P

non-pink

normal pigmentation

p

pink

black pigment removed from coat, skin and eyes, giving pink eyes

Ruby

R

non-ruby

normal pigmentation

r

ruby

black pigment removed from coat, skin and partially from eyes, giving dark maroon eyes: co-dominant with R to produce intermediate dilution and reddening of eyes

Pearl

Pe

pearl

extreme reduction in both black and yellow pigments in coat: co-dominant with pe as double Pe is lethal

pe

non-pearl

normal pigmentation: co-dominant with Pe

Mink

M

non-mink

normal pigmentation

m

mink

lightening of colour, turning black elements of coat brownish-grey

GENOTYPES OF KNOWN COLOURS:

Colour Ê

Locus ð

Agouti

Black

Colour

Dilute

Grey

Mink

Pearl

Pink

Ruby

Agouti
Reddish or greyish brown with black ticking, a grey belly and black eyes

A*

B*

C*

D*

G*

M*

pepe

P*

RR

Topaz
Golden-orange with silver ticking, silver-cream belly and dark ruby eyes

A*

B*

C*

D*

G*

M*

pepe

P*

rr

Silver Fawn
Apricot-orange with silver ticking, a white belly and red eyes

A*

B*

C*

D*

G*

M*

pepe

pp

RR

Cinnamon
Ginger/russet brown with chocolate ticking, a pale grey belly and black eyes

A*

B*

C*

D*

G*

mm

pepe

P*

RR

Cinnamon Pearl
Ticked coat banded in cream, blue and orange with silver guard hairs, appearing golden with a silver sheen, silver-grey belly and black eyes
Some pearls have an additonal sootiness gene making them darker

A*

B*

C*

D*

G*

mm

Pepe

P*

RR

Blue Agouti (Opal)
Medium fawn with blue ticking, blue underfur, a silver belly and black eyes

A*

B*

C*

dd

G*

M*

pepe

P*

RR

Blue Cinnamon (Opal)
As for blue agouti but paler

A*

B*

C*

dd

G*

mm

pepe

P*

RR

Lilac Agouti (Lynx)
Medium fawn with dove-grey ticking and pale grey underfur, all preferably with a pinkish tinge, with a silver belly and dark ruby to black eyes

A*

B*

C*

dd

G*

**

pepe

P*

Rr
or
rr

Biscuit Cream
(provisional name)
Pale, sandy taupe with blackberry eyes, and charcoal-grey spot on tip of testicles

A*

B*

c^ec^e
or
c^ec

D*

G*

mm

pepe

P*

RR

Medium Lilac
Bluish dove grey with black eyes

A*

bb

C*

dd

G*

M*

pepe

P*

RR

True Lilac (1)
Dove grey with pink tinge (a blue tinge is considered a fault) and dark ruby eyes

A*

bb

C*

dd

G*

M*

pepe

P*

Rr

True Lilac (1)
Dove grey with pink tinge (a blue tinge is considered a fault) and black eyes

A*

bb

C*

dd

G*

mm

pepe

P*

RR

Black (formerly Silver Grey)
Black, usually with a slight brown tinge, with black eyes and often with heavy silvering

aa

B*

C*

D*

G*

M*

pepe

P*

RR

Chocolate (1)
Rich chocolate brown with dark ruby or black eyes

aa

B*

C*

D*

G*

M*

pepe

P*

Rr

Buff (a.k.a. beige in Sweden)
Magnolia with dark ruby eyes

aa

B*

C*

D*

G*

M*

pepe

P*

rr

Champagne
Pale pinkish beige with red eyes

aa

B*

C*

D*

G*

M*

pepe

pp

RR

Mink
Grey with black eyes: bluish when very young, becoming brown-tinged in adulthood and tending to turn ginger around the rump in later life

aa

B*

C*

D*

G*

mm

pepe

P*

RR

Pearl
Pale oatmeal ticked with grey, sometimes darker at the extremities, with silver-cream belly and black eyes Some pearls have an additonal sootiness gene making them shaded smoky grey

aa

B*

C*

D*

G*

mm

Pepe

P*

RR

Havana (formerly ruby-eyed mocha)
Rich brown with medium ruby eyes

aa

B*

C*

D*

G*

mm

pepe

P*

Rr

Swedish ivory???
Off-white with dark ruby eyes

aa

B*

C*

D*

G*

mm

pepe

P*

rr

Graphite (a.k.a. German Blue)
Plain pencil-lead grey with black eyes

aa

B*

C*

D*

gg

M*

pepe

P*

RR

Blue (a.k.a. Russian Blue in Sweden???)
Blue-grey with black eyes - the original blues were a light, bright colour resembling the back of an African Grey Parrot, but many British blues are now a darker, duller colour

aa

B*

C*

dd

G*

M*

pepe

P*

RR

Blue-beige (Swedish variety)
Very cold pale blue

aa

B*

C*

dd

G*

M*

pepe

P*

rr

Milk cream
(provisional name)
Off-white with blackberry eyes, and charcoal-grey spot on tip of testicles

aa

B*

c^ec^e or c^ec

D*

G*

M*

pepe

P*

RR

Dark-eyed Himalayan
White with sepia points and blackberry eyes, and charcoal-grey spot on tip of testicles

aa

B*

c^ec^h

D*

G*

M*

pepe

P*

RR

Seal-point Siamese
Very pale brownish beige, often darker over the rump, with dark sepia points and ruby eyes
N.B. addition of mm produces a white-bodied Siamese, resembling a Himalayan but with darker eyes

aa

B*

c^hc^h

D*

G*

M*

pepe

P*

RR

Himalayan
White with dark sepia points and pink eyes

aa

B*

c^hc

D*

G*

M*

pepe

P*

RR

Chocolate (2)
Rich chocolate brown with black eyes

aa

bb

C*

D*

G*

M*

pepe

P*

RR

Coffee
Rich caramel, often with a grey tinge, and with black eyes

aa

bb

C*

D*

G*

mm

pepe

P*

RR

Pink-Eyed White (albino)
White with pink eyes

**

**

cc

**

**

**

**

**

**

A cold colour like a bluish champagne has been seen in self stock carrying both the blue and cream genes, but since other genes were also probably present it is not clear whether these rats were blue-creams or something else, such as blue-beige.

Agoutis and cinnamons both come in a reddish and a greyish phase. It is not clear whether this is because the darker animals are Aa; or because the red ones are Rr; or because the greyer animals have umbrous polygenes (polygenes are additional genes which alter the expression of the gene you are looking at - usually additional genes which haven't been identified yet and which you can't predict).

A black-eyed yellow gene is said to have has been recorded in laboratory rats. This may have been the Exclusion of Black gene e on the Extension of Black locus. This is a locus which controls the width of the black hair in ticked coats: mutations at this locus are found in several other rodents including the Ship rat, Rattus rattus. Homozygous ee removes the black band from the hairs without affecting the skin, so such an animal may have yellow or cream fur on a blueish agouti-type skin.

The E gene at this locus is the normal band-width, and the Dominant Extension of Black gene E^D extends the black band to cover the entire hair, giving a dense blue-black coat which is not recorded in Norway rats. In Ship rats E^D is co-dominant with E, and an EE^D animal is a steel - black on the back and dark grey-brown on the sides.

German Blue or Graphite appears to be a new dilution on its own separate locus. It has not yet been established whether or not the Russian Blues being bred in Sweden are the same as the normal blues bred elsewhere, but the likelihood is that they are.

The genetics of the ivory rats reported from Sweden are also uncertain, but they are apparently a combination of multiple dilutions including ruby.

NB In at least some paler strains of the homozygous dd blue rat there is an increased risk of does haemorrhaging severely when they give birth. In some cases this can be fatal. Unless and until this problem can be eliminated, it is safer to produce blues only by mating blue or blue-carrying (Dd) bucks to blue-carrying females.

It has been reported that a particular strain of blue rat in which haemorrhaging is present also has dark spots on the tips of the testicles, similar to those seen in rats expressing the cream gene c^e. It may be that there is a corresponding pigment-spot inside the vagina, and that this increases the risk of tearing. If this is the cause of the bleeding then it could be bred out, since not all blue bucks have testicle-spots.

It might also mean that there is an increased risk of haemorrhaging in cream does. At present there is no evidence on this one way or the other, since this is a new variety, and all the cream does who have been bred from so far were hooded and therefore white around the genitals.

EYES:

Rats described as having black eyes have a very dark brown iris - about the colour of an apple-pip - with a black pupil and retina.

In ruby eyes there is a reduction of pigment in both iris and retina, allowing the red of the blood to show through. Very dark ruby eyes, as seen in the best topazes, appear almost black: lighter ruby eyes are a clear, translucent dark red. Some experts consider that in fact all rats are ruby-eyed, and that only the depth of colour makes the wild-type eye appear brown.

Because the reduction in pigmentation of the retina can cause blurred vision, some ruby-eyed rats sway their heads from side to side in order to achieve a better focus.

Pink and red eyes are eyes without any pigment in retina or iris. The pupil is visible only as a faint ring on the surface of the eyeball, and the whole eye is clear, translucent pale red - ranging from the pinkish-red of a pomegranate seed through to a bright redcurrant shade.

The lack of pigmentation of the retina causes blurred vision, so many pink-eyed rats head-sway to improve their focus. This is not as harmful as it sounds, however, since rats rely primarily on scent and hearing: a rat with poor vision is only about as inconvenienced as a human with no sense of smell.

In blackberry eyes, as seen in creams, the eye-colour is as for normal black eyes, but the pupil tends to be kept very wide open, so that instead of the brown of the iris one sees mainly the very dense blue-black of the retina. This makes the eyes appear even darker than those of an agouti, and with a slight purple tinge. In very strong light the pupil contracts normally, and the eye becomes like a normal black (i.e. very dark brown) eye.

I have seen one instance of head-swaying in a blackberry-eyed rat (an ivory cream): so it may be that these eyes are super-dark ruby, appearing black to the human eye but still in fact having a slight loss of pigment from the retina.

Chinchilla and European-type husky (progressive roan) rats also have very open pupils, but in them there is a marked ruby-type reduction in colour from the retina, so that what one sees through the pupil is dark maroon-red rather than the blue-black of the blackberry eye. Husky rats also have a blue-tinged iris.

Locus	Code	Name	Description
Agouti	A	agouti	wild-type ticked and banded coat
Agouti	a	self	extends colour of ticking to entire hair, giving a plain unticked, unbanded coat
Black	B	black	normal colouration of black elements of coat
Black	b	brown	dilution of black elements of coat to brown
Colour	C	full colour	both black and yellow pigments (eumelanin and phaeomelanin) present
	c^e	extreme dilution	normally black band of agouti coat - or whole hair in self coat - bleached to off-white; skin pale except on ears, tail and genitals, but black freckle appearing on tip of testicles, and very dark eyes: co-dominant with c^h
	c^h	Himalayan	black pigmentation temperature-sensitive, only developing in on cold areas of body, plus partial chichillation (reduction in red pigment): co-dominant with c^e
	c	albinism	complete absence of pigmentation
Dilute	D	dense colour	normal intensity of colour
Dilute	d	dilute colour	lightening of colour, turning black elements of coat light steel-blue - this is due to eumelanin (black pigment) forming clumps instead of being evenly spread, so in fact dd animals have more eumelanin by weight than DD, and Dd animals can be slightly darker than DD
Grey	G	non-grey	normal intensity of colour
Grey	g	grey	lightening of colour, turning black elements of coat flat grey
Pink	P	non-pink	normal pigmentation
Pink	p	pink	black pigment removed from coat, skin and eyes, giving pink eyes
Ruby	R	non-ruby	normal pigmentation
Ruby	r	ruby	black pigment removed from coat, skin and partially from eyes, giving dark maroon eyes: co-dominant with R to produce intermediate dilution and reddening of eyes
Pearl	Pe	pearl	extreme reduction in both black and yellow pigments in coat: co-dominant with pe as double Pe is lethal
Pearl	pe	non-pearl	normal pigmentation: co-dominant with Pe
Mink	M	non-mink	normal pigmentation
Mink	m	mink	lightening of colour, turning black elements of coat brownish-grey

	A cold colour like a bluish champagne has been seen in self stock carrying both the blue and cream genes, but since other genes were also probably present it is not clear whether these rats were blue-creams or something else, such as blue-beige.
	Agoutis and cinnamons both come in a reddish and a greyish phase. It is not clear whether this is because the darker animals are Aa; or because the red ones are Rr; or because the greyer animals have umbrous polygenes (polygenes are additional genes which alter the expression of the gene you are looking at - usually additional genes which haven't been identified yet and which you can't predict).
	A black-eyed yellow gene is said to have has been recorded in laboratory rats. This may have been the Exclusion of Black gene e on the Extension of Black locus. This is a locus which controls the width of the black hair in ticked coats: mutations at this locus are found in several other rodents including the Ship rat, Rattus rattus. Homozygous ee removes the black band from the hairs without affecting the skin, so such an animal may have yellow or cream fur on a blueish agouti-type skin. The E gene at this locus is the normal band-width, and the Dominant Extension of Black gene E^D extends the black band to cover the entire hair, giving a dense blue-black coat which is not recorded in Norway rats. In Ship rats E^D is co-dominant with E, and an EE^D animal is a steel - black on the back and dark grey-brown on the sides.
	German Blue or Graphite appears to be a new dilution on its own separate locus. It has not yet been established whether or not the Russian Blues being bred in Sweden are the same as the normal blues bred elsewhere, but the likelihood is that they are.
	The genetics of the ivory rats reported from Sweden are also uncertain, but they are apparently a combination of multiple dilutions including ruby.
	NB In at least some paler strains of the homozygous dd blue rat there is an increased risk of does haemorrhaging severely when they give birth. In some cases this can be fatal. Unless and until this problem can be eliminated, it is safer to produce blues only by mating blue or blue-carrying (Dd) bucks to blue-carrying females. It has been reported that a particular strain of blue rat in which haemorrhaging is present also has dark spots on the tips of the testicles, similar to those seen in rats expressing the cream gene c^e. It may be that there is a corresponding pigment-spot inside the vagina, and that this increases the risk of tearing. If this is the cause of the bleeding then it could be bred out, since not all blue bucks have testicle-spots. It might also mean that there is an increased risk of haemorrhaging in cream does. At present there is no evidence on this one way or the other, since this is a new variety, and all the cream does who have been bred from so far were hooded and therefore white around the genitals.
EYES:
	Rats described as having black eyes have a very dark brown iris - about the colour of an apple-pip - with a black pupil and retina.
	In ruby eyes there is a reduction of pigment in both iris and retina, allowing the red of the blood to show through. Very dark ruby eyes, as seen in the best topazes, appear almost black: lighter ruby eyes are a clear, translucent dark red. Some experts consider that in fact all rats are ruby-eyed, and that only the depth of colour makes the wild-type eye appear brown. Because the reduction in pigmentation of the retina can cause blurred vision, some ruby-eyed rats sway their heads from side to side in order to achieve a better focus.
	Pink and red eyes are eyes without any pigment in retina or iris. The pupil is visible only as a faint ring on the surface of the eyeball, and the whole eye is clear, translucent pale red - ranging from the pinkish-red of a pomegranate seed through to a bright redcurrant shade. The lack of pigmentation of the retina causes blurred vision, so many pink-eyed rats head-sway to improve their focus. This is not as harmful as it sounds, however, since rats rely primarily on scent and hearing: a rat with poor vision is only about as inconvenienced as a human with no sense of smell.
	In blackberry eyes, as seen in creams, the eye-colour is as for normal black eyes, but the pupil tends to be kept very wide open, so that instead of the brown of the iris one sees mainly the very dense blue-black of the retina. This makes the eyes appear even darker than those of an agouti, and with a slight purple tinge. In very strong light the pupil contracts normally, and the eye becomes like a normal black (i.e. very dark brown) eye. I have seen one instance of head-swaying in a blackberry-eyed rat (an ivory cream): so it may be that these eyes are super-dark ruby, appearing black to the human eye but still in fact having a slight loss of pigment from the retina.
	Chinchilla and European-type husky (progressive roan) rats also have very open pupils, but in them there is a marked ruby-type reduction in colour from the retina, so that what one sees through the pupil is dark maroon-red rather than the blue-black of the blackberry eye. Husky rats also have a blue-tinged iris.