After having gone through the many different colours of dogs, we have come to the end of our series and are finishing off on the last gene. With help from our canine geneticist, Dr Sheila Schmutz at the University of Saskatchewan in Canada, we explain the last one, the Agouti gene. This gene has several alleles and shows a mixture of colours from clear fawn to the wild type as seen in German Shepherd dogs.
There are four different types of colours that can be caused by the Agouti gene: Wild Type Black Banded Hairs, fawn or clear sable, tricolour / black-and-tan / tan points and recessive black.
These are the alleles involved:
A (agouti) = Agouti signalling protein (ASIP)
• ay = fawn (cream to yellow to red with darker tips) and sable (some solid black hairs intermingled among reddish hairs)
• aw = wild colour of sable (alternating bands of reddish and black in the hairs)
• at = black-and-tan or brown-and-tan, tricolour or tan points
• a = recessive black
The Agouti gene
Dr Sheila Schmutz explains: “Just to complicate things, Agouti has more than one promoter which seems to signal where on the body, or even on individual hairs, each pigment is laid down (where the yellowish colour should lie and where the black should lie). Roughly, one seems to control ventral or belly colour and another dorsal or back colour. The simplest way to see this is on some black and tan dogs. You will notice that the back is black from eumelanin pigment being made and the belly is tan or red from phaeomelanin pigment being made. In some dogs banded hairs are produced over parts of the body. With certain genotypes, the coat colour changes from birth to adulthood, usually being born darker and then lightening.”
Agouti is a common name and is also known as:
• A type of rodent that is found in central America, the Common Agouti
• Another rodent found in the Amazon rainforest, the Tailed Agouti
• A domestic type of guinea pig
• A type of hormone that acts as an antagonist at melanocortin
Fawn and Sable
“This allele is responsible for the coat colour called sable in Collies and Shetland Sheepdogs. In all these breeds some solid black hairs occur. The sable, and probably all red coat colours, of the Cardigan Welsh Corgi are also caused by this allele. Note that sable in German Shepherd Dogs is a term used to describe the presence of banded hairs and is not caused by this allele, but instead by the aw allele as described above,” says Schmutz. This allele is also seen in Whippets, Great Danes and Pugs.
“Although many dog breeders have assumed that the differences in darkness of fawn or sable dogs is determined by whether they are homozygous or heterozygous for ay, it is now known that some to all of this variation is caused by another gene,” says Schmutz.
Famous Agouti dogs
• Strongheart the German Shepherd. He was one of the earliest doggy film stars even before Rin Tin Tin, who is now considered to be the most famous doggy film star. He even has his name on the Hollywood walk of fame
• A Pug named Frank was the star in the popular movies Men in Black and Men in Black 2
• The famous Rough Collie that I am sure everyone knows, Lassie
• The comic strip Garfield features the irritating dog Odie. Odie is in fact a Beagle
Wild Type Black Banded Hairs
This hair comes from wolves and coyotes and is yellowish with a black tip and base. “The competition, in that case, is going on as the hair is growing which results in a hair that changes colour along its length. This gene is likely also causing the change in hair colour in the Malamute, Siberian Husky, the Silky Toy Terrier, and some German Shepherd Dogs,” says Dr Schmutz.
Recessive black occurs when a German Shepherd Dog inherits the recessive genotype responsible for an all-black coat colour. This gene is uncommon in other non-herding breeds but in this particular breed, it can be quite common. It occurs in some other herding breeds, such as Groenendael and Shetland Sheep dogs.
Tri-colour, black and tan, and tan points
Gordon Setters are clear examples of a black and tan dog. Tan points are just that – points of tan on a dog. “Most often the tan is located in specific body regions or points and called a ‘tan point’. Tan points, however, are more difficult to distinguish on brown-and-tan Brittany Spaniels but are still visible. On an orange English Setter, they can be impossible to detect.”
Although Beagles look like they are tri-colour, some of them are not. Beagles who have saddles, which are usually black, are thought to have a different allele. This allele was called as by Willis and he used it to describe Beagles and Dachbrackes rather than describing them as black and tan with white. “Whether this is a separate allele or is a modification of the black-and-tan pattern by another gene, is not yet known,” says Schmutz.
As I am sure you are aware, there is still much to be learnt in the confusing world of canine genetics, but thanks to people like Dr Sheila Schmutz and Clarence C Little we are able to learn more and understand our dogs from a different and interesting angle.
For more information on dog genetics and the colours that genes and alleles produce, visit Dr Sheila Schmutz’s website http://homepage.usask.ca/~schmutz/dogcolors.html
Text: Kerry de Bruyn
Photography: Johann Theron
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