The A locus is responsible for a number of common coat patterns in the dog. Expression of all of them requires any combination of two Ky or Kbr alleles at the K locus, and at
least one E or EM allele at the E locus. The gene involved is the Agouti gene,
and variations in it are responsible for fawn and sable dogs (Ay),
wild type (aw), tan points (at), and recessive black(a).
analysis proves absence or presence of the mutation typically responsible for fawn or sable. In fawn/ sable dogs this test shows if other agouti alleles are present
but hidden (only one copy of Ay). It also demonstrates how many
copies of this allele are hidden in dogs, which cannot express agouti types (KBKB, KB kbr, KB ky,
at the k locus and/or ee at the E locus).
shows whether a black dog is black due to “recessive black,” or the more common black
at the K locus. It also reveals whether a non-black animal carries “recessive
black.” (e.g. German Shepherd Dog, Shetland Sheepdog)
at allele (tan points, tricolors)
There is no direct test yet for this recessive allele (, but in some breeds, carriers may be deduced by use of the other two agouti tests.
In breeds where only the Ay and at alleles
are present, the Ay test can be used to see if the fawn/sable dog is Ay/Ay (homozygous)
or only has one Ay (heterozygous).
If it only has one, the other allele must be at.
Collies, Cardigan Welsh Corgi, Dachshund, Norwich Terrier, Staffordshire
Terrier) In breeds where
only Ay, at and
“a” alleles are present, both the Ay test
and the “a” test need to be performed. Any alleles unaccounted for by these two
tests will be at. For example, if a dog is Ay/Ay both
alleles are accounted for. If a fawn/sable dog only has a single Ay,
then the other allele must either be an “a” or an at, and this can be
determined by running the recessive black (“a”) test. Examples of breeds:< Shetland
Sheepdog, Belgians (Malinois, Groenendael).