THE LIVER GENE
The liver gene occurs on the B locus. It is recessive, so b is liver and B is non-liver, and in order for a dog to be liver it must have the genotype bb. This means that a liver puppy can be born from black parents if both are carriers of the liver gene (i.e. if both are Bb then at least one pup in four will be bb).
The different pigment colour genotypes are:
BBdd or Bbdd - blue (non-liver, dilute)
BBDd or BBDD - black (non-liver, non-dilute)
bbdd - isabella (liver, dilute)
bbDd or bbDD - liver (liver, non-dilute)
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). Sometimes a liver dog can also have a pink nose. See the nose and eye pages for more information and examples.
Black nose (left) and liver nose (right).
Brown eyes on a black dog (left) and amber eyes on a liver dog (right).
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. This pigment colour will be visible in the nose leather. Black, blue, liver or isabella pigment simply means that IF a dog has eumelanin in its coat, it will be that particular colour. If there is no eumelanin in the coat, there will, in most cases, be eumelanin in the nose and eyes, so the pigment colour can still be identified. Phaeomelanin (red) never affects the nose or eye colour, only the coat.
This English Springer Spaniel, Dunder, has a very dark liver coat and dark amber eyes. If it wasn't for his nose, he would look almost black in many photographs, which
just goes to show how important noses are when identifying eumelanin pigment colour! Dunder and his photo belong to Nova.
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. It is not thought that the particular liver gene carried by a breed affects its colour, however. The differences in shades of liver are probably caused by other modifiers.
EXAMPLES
Solid liver.
Liver with white markings. The German Spitz is a piebald with clear white. The English Springer Spaniel has light to medium ticking on its legs and muzzle.
The two German Pointers show the liver roan colouration on a piebald pattern. The Dalmatian has liver spots, which are a modified form of ticking.
Liver with traditional tan markings (bbatat). The last dog, a Bloodhound, has the creeping tan pattern. The genetic basis for this
is unknown, but it appears to be connected to both tan points and saddles.
Liver shading. These dogs are probably sables, grizzles or wolf greys with the red in the coat turned to white by one of the chinchilla genes, leaving
just liver shading on white.
Liver merles (bbMm).
Red dogs with liver pigment. All of these dogs are either liver sables (bbayay) or recessive reds with liver pigment (bbee)
"RED" AND "CHOCOLATE"
Sometimes liver is given different names. In the Labrador it is known as chocolate, and in some breeds it is known as red or brown. Liver merles are also called "red merles". This is an incorrect term. "Red" is, in genetic terms, phaeomelanin, not eumelanin, so be careful when using terms such as "red merle" and make sure you know what they actually mean. There is no such thing as an actual "red merle", because the merle gene does not affect red pigment (phaeomelanin), only black, liver, blue and isabella (eumelanin). Sometimes liver dogs with tan points and white markings are also called "red tricolours" - again, this is a misleading and incorrect term.
LIVER LOOK-A-LIKES
There is a dark shade of red (phaeomelanin) which can look very similar to liver. This colour is mainly found in Irish Setters and Welsh Springer Spaniels. These dogs can be distinguished from livers by their black nose pigment (technically a dark red could have liver pigment, but it's likely that their phaeomelanin would be affected slightly and they would end up a lighter colour than a black-pigmented red).
Also be careful not to mistake a solid black dog for a liver. Of course, this sounds silly - how could you mistake black for liver? Well it's actually surprisingly easy to in longhaired breeds. When a black dog has long hair, the hair can turn a brownish shade, particularly if the dog is outside for long periods of time. This is called bronzing, and has no genetic base, but is purely environmental. In a photograph, bronzing can make it very difficult to tell whether a dog is black or liver, but in the flesh, you should be able to tell by the nose colour.
Lastly, there is a colour called seal which can make a dog look brownish in certain lights. Seal is probably located on the A locus with the agouti colours, but it's not known for sure. It consists of a black topcoat and a reddish undercoat, so when the undercoat shows through the dog can look almost liver. At other times, the dog can look solid black. Seal is a very rare colour which only appears in a handful of breeds, and consequently very little research has been done on it.
All of the gundogs above (a Welsh Springer Spaniel and two Setters) show a deep red colouration (almost certainly recessive red, ee), but none are liver.
The Poodle at the end has a very similar reddish coat to the Setters, but in fact this dog is a true liver (bb), showing just how difficult it can
sometimes be to tell liver and red apart. In general, liver is duller and more chocolatey than red, but it seems there are exceptions.
The Chow Chow on the left shows very extensive bronzing. Much of the coat has been bleached to brown. The dog in the middle is my own dog, Rosie. She has
what appears to be bronzing on her muzzle, and in sunlight the long fur on her neck and back shines brown. The last dog is a Bergamasco with bronzing on the ends of its cords (the oldest parts
of the hair are at the ends of the cords, and these have therefore had the most exposure to sunlight).
This Shar Pei shows the seal colouration. Many dogs with less thick coats do not show seal so well - they appear more black than this dog does. The
similarity with the Chow Chow above suggests that the Chow may in fact be seal too, but it is difficult to tell.