You are here: Home > General Dog Information > Colour Genetics

Colour Genetics

What is Colour

There are two types of pigment which create coat colour in dogs, Eumelanin and Phaeomelanin. Pigment gives each strand of hair its colour. All coat colours and patterns in dogs are created by two pigments. Each of the pigments has a "primary" colour, these primary colours are then altered by various genes which gives us colour variations.

Pigmentation Descriptions

The first and most important pigment is Eumelanin is black pigment. All black areas on a dog are caused by cells producing eumelanin. However, there are genes which turn eumelanin into other colours - liver (brown), blue (grey), or Isabella (a dusty pale brown). If a dog has any of the genes to turn its black eumelanin into liver, blue or Isabella then all of the black in its coat will be changed. Blue and Isabella dogs are referred to as "dilutes". They either lack the genes which tell their cells how to produce proper eumelanin, or their cells know how to produce it but can't.

A black nose, eye rims, lips, nails and pads means the dog is Black pigmented", "liver pigmented" and produces black eumelanin.

As well as being found in the coat, eumelanin is present in the other parts of the dog that need colour - most notably the eyes (irises) and nose. The nose will be black, liver, blue or Isabella depending on the type of eumelanin the dog can produce. The colour in irises is produced by layers of pigment, and brown eyes like most dogs have are, caused by black eumelanin in those layers. When a dog has altered/restricted production of eumelanin, the irises are also unable to produce full-strength eumelanin. This means that the dark pigment in the eye becomes lighter, and the eyes turn into a light brown colour, known as amber or gold.

The second pigment is Phaeomelanin. This is red pigment. The term "red" covers everything from deep red (like Irish Setters) to light cream, encompassing gold, yellow, tan and orange.

Phaeomelanin is produced only in the coat. It does not occur in the eyes or the nose, so any genes which affect the colour/intensity of phaeomelanin will not affect the eyes or nose. Only eumelanin occurs in those areas, and so only genes which affect eumelanin can affect the eye or nose colour.

White

White isn't colour, white hair on animals is caused a lack of pigment. It is a lack of both eumelanin and phaeomelanin. White areas on animals are caused when cells don't produce any pigment. Sometimes the whole animal is affected, like in albinos, and sometimes just parts of it are affected, like in dogs with white markings. It can affect the production of eumelanin in eyes and noses too, turning noses pink and eyes blue (or red in proper albinos).

There is a second type of white, which is caused by a gene called chinchilla. The chinchilla gene dilutes red (phaeomelanin) pigment, making the cells produce less pigment particles than normal, so the colour gets lighter. If it is diluted enough, it can become white. Many white dogs have a slight ivory/cream sheen to their coats because their cells are still producing a very small amount of pigment. This sort of white does not affect eumelanin, so any black/liver/blue/Isabella areas on the coat will stay dark, as well as the eyes and nose. 

Distribution Of Pigment

The colour genes in dogs do two things - they determine the eumelanin and phaeomelanin colours/shades, and they control the distribution of these two pigments.

The Colour Genes

I have only discussed the primary colours gene that are associated witht he Swedish Vallhund.  The Brindle and Merle factors are not discussed here.

There are two colour markings - solid (no tan markings, just eumelanin) or non-solid (tan markings of any sort). These colour markings depends on the K locus. K consists of three genes:
K - dominant black (solid black, no red)
k - recessive non-black (will have black nose pigment and may have black markings, but may have red markings)
kbr - brindle  

A dog with even just one K gene will be solid black.  A dog with two k genes (i.e. homozygous for k) will show tan markings which are determined by locus, A (Agouti series).

Ay - sable
aw - agouti
as - saddle pattern
at - tan points
a - recessive black

A locus, can be overridden by other genes, such as liver, dilution, greying and merle. All of these will alter the way a dominant black dog looks, but the one thing they cannot do is add phaeomelanin (red) to the coat. The only way phaeomelanin can be added to the coat of a dog with the dominant black gene is through the e gene (E locus) - recessive red. This turns a dominant black dog (or indeed, any dog) into a solid red dog with black nose pigment.

The liver gene affects eumelanin (black) only. All of the black in the coat will be turned to liver when a dog is bb on the B locus. This includes saddles, shading, merle etc. It is genetically impossible for a liver dog to have black or even grey in its coat, or for a black or blue dog to have liver in its coat. The entire coat on a liver will be shades of brown, with red (tan) or white according to the other genes present. Liver also turns the nose brown and the eyes amber (or light brown).

The nose colour is the main way to tell a liver from a black or blue. Sometimes dogs are born with only phaeomelanin (red) in their coats (for example, sables or recessive reds), but these dogs will still have one of the eumelanin pigment colours - black, blue, liver or Isabella. Every single dog can be said to be black, blue, liver or Isabella, whether or not they have any in their coat. Phaeomelanin (red) never affects the nose or eye colour, only the coat.

Although we deal here with just the genes b and B, it has actually been found that there are a variety of different recessive genes which cause liver, all located on the B locus. These are often labelled bc, bd and bs. Many breeds carry more than one of these genes, bs and bd being the most common, and bc being the rarer type.

The Dilution Gene

The dilution gene occurs on the D locus. It is recessive, so d is dilute and D is non-dilute. In order for a dog to be dilute it must have the genotype dd. A dog which is Dd or DD will have normal pigment.

The dilution gene affects eumelanin (black and liver).  A black dog with the dilution gene becomes blue and a liver dog becomes Isabella. A blue or Isabella can have any coat pattern, but whatever they have, any black or liver in the coat will be turned to blue or Isabella. It is genetically impossible for a blue dog to have any black in its coat, or for an Isabella to have liver.

Blue

Black dogs become blue when they are dd on the D locus. Blues can range from silver to almost black, and it can be difficult to tell a blue from a black by just looking at photographs. However, when the dog is actually examined, it should be obvious that the nose is blue. The coat may be entirely sable or recessive red, but if the dog has a blue nose, it is genetically blue.

Isabella

The same dilution gene that causes a black dog to become blue also causes a liver dog to become Isabella, which is a pale greyish brown. Dilution and liver are both recessive and relatively rare, so Isabella is a rarely seen colour. An Isabella dog will have the genotype bbdd (homozygous for liver, homozygous for dilution).

The Agouti Series

Broadly speaking, the agouti series controls which cells produce eumelanin (black pigment) and, in the case of the agouti gene itself, when. The pattern of the spread of black hairs is followed by all of the genes in the A series (with the exception of recessive black).

In its normal form, agouti can be almost identical to shaded sable. The main difference is the banded hairs.  When combined with one of the chinchilla genes (see the C locus), agouti becomes much more distinctive. Chinchilla dilutes red pigment (phaeomelanin), so the red hairs on an agouti dog become cream or greyish. The result is a grey dog, like the Keeshond or the Elkhound.

Sable (Ay) is dominant in the agouti series, so a dog only needs one sable gene to express it. There are three types of pattern that can be caused by this gene, but it's not certain what causes each one to appear. It's probable that sable is simply affected by (as yet unidentified) modifiers.

The three patterns are: clear sable, tipped sable and shaded sable.

Clear sables are completely red dogs with just a few black hairs. They can be almost impossible to distinguish from recessive red dogs (see the E series) unless they have a black mask (Em), which never appears on recessive reds (because they're unable to produce any black hairs). If there is any black in the coat at all, the dog must be a sable rather than a recessive red.

Tipped sables are red dogs with black hairs, usually on the back, head and tail. It seems that most tipped sables also have black masks (Em), so it's possible there is a link between the two genes (although not all masked sables have tipping).

Shaded sables are red dogs with brown and black hairs covering the top of the head, ears and back, in a distinctive pattern similar to the pattern seen on dogs with creeping tan (see below). The shading can be very light (just some scattered dark hairs forming a rough pattern), or very dark and distinct. A distinctive feature is the "widow's peak" on the forehead, where the brown forms a point. Shaded sables are known simply as "sables" in breeds like the Shetland Sheepdog and Rough Collie, and "grizzles" in Salukis. It's also likely that "domino" Afghan Hounds are in fact shaded sables 

The Mask Gene

Eumelaninistic masks (black on the muzzle and sometimes the ears) are caused by the Em gene, which is found on the E locus. It is the dominant of the E series, so that means a dog only needs one Em gene to have a mask, regardless of which other E locus gene it carries. Genotypes for masked dogs are, therefore, as follows:
EmE - one mask gene, one normal extension gene
Eme - one mask gene, one recessive red gene
EmEm - two mask genes


If a dog does not have a mask, it must have the genotype EE (two copies of the normal extension gene), Ee (one copy of normal extension, one of recessive red), or ee two copies of recessive red. 

Masks consist of eumelanin (black pigment), so can be affected by any gene that changes the colour or intensity of eumelanin. This means a mask can be liver, blue or Isabella, and can show the merle pattern.

Recessive Red

The other two E locus genes are E (normal extension) and e (recessive red). Normal extension simply allows a dog to express its other genes on other loci normally, it has no effect on the dog. Recessive red, however, produces a much more visible effect.

A dog which is homozygous for recessive red, genotype ee, will be completely red. Its nose will remain black (or liver, blue or Isabella, whatever its eumelanin pigment colour is), and so will its eye rims and lips, but the rest of its coat will be solid red (with or without white markings and ticking). This is because the recessive red gene, in effect, gives the skin cells a disability - it stops them from being able to produce eumelanin. It is impossible for a recessive red dog to have any black (or liver, blue or Isabella) in its coat.

Recessive red, although recessive in its own series, is dominant over almost everything else. Dominant black, sable, tan points, saddle markings, wolf grey, merle, and any other pattern with black in it will be turned to solid red by the recessive red gene. It's impossible to know from looking at a recessive red dog whether it carries sable, tan points, brindle, or any other A or K locus gene, and so impossible to know what it will pass down to its puppies unless you know its family history.

Chinchilla, Extreme Chinchilla And Platinum

Chinchilla causes dilution of red (phaeomelanin) pigment to a lighter shade of tan or yellow. Eumelanin (black, liver, blue, Isabella) is not affected. Extreme chinchilla causes further dilution, usually to cream or light yellow, and platinum is dilution to white (usually with a slight yellowish sheen).

Very little is known about these three genes. It is possible that they display incomplete or co-dominance, which would account for the extreme variations in shade. A cchcp (one copy of chinchilla, one of platinum) dog would therefore appear to be around the colour of a dog with extreme chinchilla (ce), but possibly slightly darker.

The chinchilla series is thought to be responsible for solid white dogs with black nose/lip/eye-rim pigment, such as Samoyeds. These dogs are recessive red (ee) with the platinum gene, which dilutes their phaeomelanin (red) to white.

The White Spotting Series

White spotting on dogs is determined by the genes on the S locus. When we use the term "white spotting" we simply mean white areas, not actually white spots. White spotting can occur on any colour, and will cover up both eumelanin and phaeomelanin. So any dog can have white markings, whether they're black, blue, liver, Isabella, brindle, sable, tan-pointed, merle or whatever.

White hair occurs when the skin cells are unable to produce any pigment. The white spotting gene impairs the ability of cells on particular parts of the skin to make pigment, so the skin becomes pink and the fur white. Nails and paw pads will also become pink in areas where pigment is not produced.

There are generally thought to be four alleles on the S locus, each causing different amounts of white. However, these do not seem to account for the huge variation in markings seen on dogs, so it's possible there are more which haven't yet been identified. The four that geneticists are pretty sure exist are:
S - no white
si - Irish spotting
sp - piebald
sw - extreme white (or extreme piebald)

The white spotting genes are all thought to be examples of incomplete dominance. This means that a heterozygous dog will express its most dominant gene, but will also be affected by the more recessive one. For example, if one gene is extreme white (sw) and the other is Irish spotting (si), the resulting dog will have more white than a normal Irish spotted dog. In this way, a dog could seemingly have Irish spotting or piebald markings without actually possessing the Irish spotting or piebald genes.

Nose Colour

The default nose colour for dogs is black:

Blue (dd) dogs have noses ranging from light grey to almost black. It is genetically impossible for a blue dog to have a brown nose. Note, however, that sometimes grey dogs can occur that don't have the blue dilution gene. So an apparently "blue" dog may have a black nose and dark eyes, because in fact it is a black dog with the greying gene rather than a proper blue dilute. Sometimes blues can also be very dark, so that their coat and nose appear almost black. It can be very difficult to tell whether such dogs are blacks or blues.

Liver (bb) dogs and dilute liver (Isabella, dd) have noses ranging from deep brown to pink. It is genetically impossible for a liver dog to have a black or blue nose.

Dudley Nose

Usually used to describe a dog with pigment loss on its nose.
Generally the pigment loss on a Dudley nose is in the middle of the nose, spreading outwards to cover almost all of the nose on some dogs. The pigment loss causes the nose to become lighter in these areas, usually ending up as a dull pink. Dudley noses never lose their pigment completely and are never as bright pink as butterfly noses or even the pink noses found on liver dogs. There is also always a darker area remaining around the edge of the nose. 

Snow Nose

Also known as a "winter nose", this is a Dudley nose that appears during the winter months, or sometimes as a result of stress or other factors. Dudley noses are permanent, but snow noses are not.

Links to website with more detail on Colour Genetics

http://homepage.usask.ca/~schmutz/dogcolors.html

http://bowlingsite.mcf.com/genetics/genetics.html

http://www.labbies.com/genetics2.htm 

http://www.vetgen.com/canine-coat-color.html

http://nicholescritters.homestead.com/malcolorgenetics.html

 

 
Account *

Password *