A-a Locus (A-a Locus)
The A Locus (agouti series) interacts closely with the E, K, and B Loci that can lead to a dog’s overall coat color and pattern. A Locus mutations are only expressed if the dog is “Clear” or “Carrier” at the E locus and “Clear” at the K-KB locus. There are three potential mutations at the A Locus that can each have a different effect on coat color. The mutations are known as A-ay, A-at and A-a and can determine whether a dog is a Carrier of sable/fawn, black and tan/tricolor/tan points coloration or a recessive form of a solid black or bicolor coat color.
The A-a Locus mutation results in a dog that is solid black. To confirm the source of the black coat, this also requires testing for the K-KB Locus to determine if the black color is derived from the dominant K-KB mutation or the recessive A-a mutation. A common example of the effect of this mutation is typically seen in solid black German Shepherds.
A (CLEAR/NORMAL): These dogs have two copies of the normal gene and the effect of A Locus on their coat color can be determined by testing at the A-ay and A-at loci. They will also not pass this mutation to any of their offspring.
B (CARRIER/NOT AFFECTED): These dogs have one copy of the normal gene and one copy of the mutation associated with this disease. They will not develop a solid black or bicolor coat due to this mutation and the effect of A Locus on their coat color can be determined by testing at the A-ay and A-at loci. They will, if bred, pass the mutation to 50% of their offspring, on average.
C (AT RISK/AFFECTED): These dogs have two copies of the mutation and will typically develop a solid black or bicolor coat due to the A-a locus mutation and will pass this mutation to 100% of their offspring. However, this dog’s coat color is also dependent on the E, K, and B Locus genes.