A-At Locus (A-At 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-at gene mutation produces a coat pattern typically referred to as “tricolor” or “black-and-tan”. For dogs that are “Clear” at the K-KB Locus and have two copies of the A-at mutation or one copy of the A-at mutation and one copy of the A-a mutation will express this coat pattern. This also means a dog that appears tricolor or black-and-tan can carry the A-a allele and would not express recessive black. This is due to the fact that the A-Locus alleles are expressed in a hierarchical manner with A-ay being dominant to and expressed over A-at and A-a. It is important to note that the dog’s coat color is also dependent on the dog’s genotypes at E, K, and B Locus among others.
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-a locus. They will also not pass this mutation to any of their offspring.
B (CARRIER/AFFECTED): These dogs have one copy of the normal gene and one copy of the mutation associated with tricolor or black-and-tan. They will exhibit a tricolor or black-and-tan coat pattern in the absence of the A-ay mutation. However, this dog’s coat color is also dependent on the E, K, and B Locus genes. 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 develop a tricolor or black-and-tan coat pattern due to the A-at 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.