AMATERSU'S GSD GENES GUIDE
Agouti Series
A - Locus:
This locus is thought to contain six variations, and in most discussions about GSD color this is the location (locus) we are concerned about. The variations will be listed in order of dominance, from the most dominant to the most recessive (meaning that a variation mentioned higher in the list will be expressed in the physical make up of the dog (phenotype) even when it is paired with a variation lower on the list).
A - Dominant Black. Can also be called a 'dominant self-colour'.
ay - Golden. A rarely seen version of 'sable'. Can aldo be called 'agouti'.
aw - Gray (or Sable). Both gray and red sables are genetically the same at this locus.
as - Saddle. Our common 'black and tan' german shepherds. Extended saddles are not to be confused with 'bi-colour.
at - Bicolour. Some breeders think that 'as' extended saddles are called bicolour, but aren't.
a - Recessive Black. It's much more common than 'dominant black'