Affected Genes: ASIP
 Transmission: Autosomal (Ay > aw > at > a)
Mutation:
  
Ay = A>G, Chr24:23393514, T>G, Chr24:23393510
  
aw/at = 239 bp insertion, Chr24:23365283-23365284
  
a = C>T, Chr24:23393552
Description:
Genetic testing for the Agouti locus (A locus) detects variants of the ASIP gene: Ay, aw, at, and a. These tests determine whether a dog carries:
The Ay allele, responsible for sable or fawn coat color (Ay/Ay, Ay/aw, Ay/at, or Ay/a)
The aw allele, responsible for wolf-grey, sable, or agouti coats (aw/aw, aw/at, or aw/a)
The at allele, which produces black and tan, tricolor, or tan point phenotypes (at/at or at/a)
The a allele, which prevents Agouti gene expression, resulting in a solid black coat (a/a)

References:
Dreger DL, Parker HG, Ostrander EA, Schmutz SM. Identification of a mutation that is associated with the saddle tan and black-and-tan phenotypes in Basset Hounds and Pembroke Welsh Corgis. J Hered. 2013 May-Jun; 104(3):399-406. PubMed: 23519866