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A-Locus (Fawn/Sable, Tricolour/Tan Points, Solid Black)

Description:

The agouti-signalling peptide (ASIP) gene has four different alleles that affect the pigmentation of coat colour in dogs. In dogs that do not carry the dominant black gene (ky/ky at the K Locus) and are not "e/e" for the E Locus, the agouti gene is allowed to express and determines the colour of the dog's coat. The four alleles work as a hierarchy, with the most dominant allele that the dog has always being expressed (assuming n/n for the K Locus). The most dominant allele is "ay", followed by "aw", then "at", then "a."


While the Agouti gene (A Locus) does determine the base coat colour in dogs that are ky/ky for Dominant Black, the colour of the dog can still be modified by other genes, such as the B Locus or D Locus. For example, a dog that is "b/b "for the B Locus will still have all areas that would be pigmented as black modified to a chocolate pigment. Thus a fawn dog that is also "b/b" will just show a chocolate nose, whereas a dog that is "at/at" will be chocolate and tan, rather than black and tan.

 

The "ay" Allele

The "ay" allele is the most dominant of all four alleles. The "ay" gene produces a coat colour that can range from a light fawn to darker red to a sable. This variation of colour is due to variance in expression of this gene. A dog (ky/ky for K Locus) that has one or two copies of the "ay" allele will always express the "ay" coat pattern. Thus, a dog that appears fawn or sable could be carrying any other of the three alleles, and would never express them. However, that does not mean they will always pass on a copy of the "ay" allele; a dog that is ay/aw, ay/at, or ay/a has a 50% chance of passing on the "ay" allele, and a 50% chance of passing on the other allele. A dog that has two copies of the "ay" allele will always pass on that "ay" allele, and as long as that dog is bred to another dog that is "n/n" for the K Locus, will always produce fawn/sable pups.

 

The "aw" Allele

The "aw" allele produces a colour known as "wild sable," sometimes called the "wild type," or in some breeds, "wild boar." With this colouration, the hairs switch pigmentation from black to reddish or fawn. This colour is sometimes seen in German Shepherds and other shepherd breeds. It is recessive only to the "ay" allele. If a dog is "n/n" for the "ay" allele, a dog with one or two copies of the "aw" allele will express this colouration. A dog that is n/n for "ay" that has one copy of the "aw" allele can carry either the "at" or "a" allele and not express it, though can pass either allele to any offspring.

 

The "at" Allele

Both the "black-and-tan" and "tricolour" phenotypes are caused by the "at" allele. A tricolour dog is "black-and-tan", plus white, which is generally just an absence of colour, rather than being a different pigment the dog is making. For a dog to be a black-and-tan or tricolour, he must be "n/n" for the dominant black gene, and have either two copies of the "at" allele, or have one copy of the "at" allele and one copy of the "a" allele. This is because the "ay" and "aw" alleles are dominant over "at." A dog that is"at/at" will always pass on a copy of the "at" allele to any offspring. However, he must be bred with another dog that has at least one copy of the "at" allele to possibly produce any black-and-tan or tricolour pups.

 

The "a" Allele

A dog that is solid black, but is also "ky/ky" for the K Locus, must have two copies of the "a" allele. This is also the case for dogs that are bicolor, but are negative for K Locus. This is generally the cause of a solid black German Shepherd. The "a" allele is sometimes referred to as the recessive black gene. Because this allele is the most recessive, for a dog to express this phenotype he must have two copies of the "a" allele. A recessive black dog will always pass on the "a" allele to all offspring.


Genotype Coat Colour Hidden Colour
ay/ay Fawn/Sable None
ay/aw Fawn/Sable Wild Sable
ay/at Fawn/Sable Tricolour/Tan Points
ay/a Fawn/Sable Solid Black/Bicolour
aw/aw Wild Sable None
aw/at Wild Sable Tricolour/Tan Points
aw/a Wild Sable Solid Black/Bicolour
at/at Tricolour/Tan Points None
at/a Tricolour/Tan Points Solid Black/Bicolour
a/a Solid Black/Bicolour None

The Agouti gene is only visible in dogs that do not carry the dominant black gene. The dog can still carry any of the agouti alleles. However, this effect is hidden by the dominant black gene.

A Locus Testing:

Animal Genetics UK currently offers tests for the "Ay", "At", "Aw" and "a" allele. Dogs can be DNA tested at ANY age.

Sample Type:

Animal Genetics accepts buccal swab, blood, and dewclaw samples for testing. Sample collection kits are available and can be ordered at Canine Test Now.

Testing Is Relevant for the Following Breeds:

All breeds.

Results:

Animal Genetics UK offers DNA testing for all alleles individually, or all four together for a comprehensive A-Locus genotype. The genetic test verifies the presence of the dominant or recessive allele and presents results as one of the following:

ay-Allele Results:

ay/ay The dog carries two copies of the dominant Ay allele. The dog will have a fawn or sable coloured coat if ky/ky and will always pass on the "Ay" allele to any potential offspring. All offspring will also be fawn or sable dogs if bred to another ky/ky dog.
n/ay One copy of the dominant Ay allele is present. The dog will have a fawn or sable coat colour if ky/ky and can pass on either allele to potential offspring.
n/n The dog does not carry the Ay allele, and will not have a fawn or sable coat pattern.

aw-Allele Results:

aw/aw The dog carries two copies of the wild sable allele. The dog, if ky/ky, will exhibit the wild sable phenotype, and will always pass on the wild sable allele to any offspring.
n/aw One copy of the aw allele is present. The dog can pass on either allele to potential offspring.
n/n The dog does not carry the aw allele, and will not have a wild sable coat pattern.

at-Allele Results:

at/at The dog carries two copies of the at allele. The dog will have a black and tan or tricoloured coat if the dog is ky/kyand will always pass on the at allele to any potential offspring.
n/at One copy of the dominant Ay allele is present. The dog will have a fawn or sable coat colour and can pass on either allele to potential offspring.
n/n The dog does not carry the Ay allele, and will not have a fawn or sable coat pattern.

a-Allele Results:

a/a The dog carries two copies of the recessive solid black allele. The dog will have a solid black or bicolour coat, and will always pass on a copy of the allele to future offspring.
n/a Only one copy of the recessive solid black allele is present. The dog will not express the recessive black coat colour. However, the dog can still pass on a copy to any offspring.
n/n The dog does not carry the recessive solid black allele. The dog will not express the recessive black coat colour and cannot pass it on to any offspring.