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 – see the Breeding page).
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 pigment) 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 even one black or even grey hair in its coat, or for a black or blue dog to have liver in its coat (although bronzing and seal may appear liver). 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.
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 of Livers
Liver with white markings. The Pointer is a liver piebald with slight ticking. The English Springer Spaniel has light to medium ticking on its legs and muzzle. The Dalmatian has liver spots, which are a modified form of ticking (see the Ticking page).
The two Cocker Spaniels shown here are an excellent example of the effect of the liver gene. Both are piebalds with roaning, but the dog on the left is a dominant black without the liver gene and on the right is a dominant black with the liver gene.
Liver with traditional tan markings (bbatat). The Australian Shepherd also has white markings in the trim / irish spotting pattern.
Liver grizzle/agouti. With the red/tan in the coat turned to white by the Intensity locus, these dogs are left with just liver shading on white.
Liver merles (bbMm), with tan points (atat).
Red dogs with liver pigment. All of these dogs are either liver sables (bbayay) or recessive reds with liver pigment (bbee)
Liver with the greying gene.
“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 commonly 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 can be misleading.
There is a dark shade of red (phaeomelanin) which can look very similar to liver. This colour is mainly found in gundogs such as the Irish Setter and Welsh Springer Spaniel. These dogs can be distinguished from livers by their black nose pigment (technically a dark red could have liver pigment – see below).
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. 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. See the K locus page for more information on seal.
All of the gundogs above show a deep red colouration (almost certainly recessive red, ee), but none are liver. The Aussie has a very similar reddish coat, 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.
These three greyhounds and lurchers show either seal or extensive bronzing. Notice how their noses remain black. Technically liver dogs can be seal too, and would probably appear lighter than a normal liver.
“Dog Coat Colour Genetics.” Dog Coat Colour Genetics. N.p., n.d. Web. 24 June 2014.