02/15/2022
New A locus testing, significant for wolf sable Pomeranians!
Short version:
There have been new discoveries about the A locus, and now improved testing is available! This will be VERY relevant for wolf sable breeders. Some of the dogs that previously tested „wrong“ (inconsistent with their phenotype) should now come back correctly.
Announcement by UC Davis with video and links to the study and to their info page: https://www.facebook.com/ucdavisVGL/posts/1467551530426065
Long version:
SOME BASICS
Dogs have pheomelanin (red pigment) and eumelanin (black pigment).
The amount and distribution of black vs. red pigment is governed by several genes, mainly the A, E and K loci.
The A locus (ASIP gene) plays an important role here, deciding where on the body and on each hair (banding pattern) black or red pigment is to be placed.
The shade of pheomelanin (how dark red or light cream/white it is) is influenced by several genes, often called the intensity loci. One of them (MFSD12) can be tested at several laboratories. Embark is the only lab so far that offers results for 5 different genes influencing shade of red, though those 5 still don’t explain all of the variety we see.
COLOR TERMS IN THE POMERANIAN BREED
Breed terms and genetic terms are often not exactly the same, and breed standards sometimes have requirements that go beyond the simple genetic loci we know.
As far as I am aware, the Pomeranian breed uses:
- Red, orange, cream and white for e/e (recessive yellow) dogs of different pheomelanin intensity.
- Red, orange, and cream for clear Ay (dominant yellow, clear fawn/sable) dogs of different pheomelanin intensity.
- Shaded red, shaded orange, and shaded cream for shaded Ays (shaded yellow, shaded fawn/sable) dogs of different pheomelanin intensity.
- Shaded red, shaded orange, and shaded cream for some aw (agouti) dogs of different pheomelanin intensity.
- Wolf sable for aw (agouti) dogs with very light pheomelanin.
That means that some terms are used for 2 different genotypes. That can lead to confusion.
There is no widespread term for agouti dogs of darker pheomelanin, and there is no clear distinction between e/e and clear Ay.
Note that while the A locus alleles are distinct entities, the shade of red is a continuum and subject to personal interpretation.
OLD AND NEW ASIP TESTING
In the past, many breeds have reported unexpected or straight „impossible“ A locus results, like visibly tanpoint dogs that test as aw/aw, or agoutis that test as Ay/- and so on. This was especially prevalent in Northern and Spitz breeds.
In 2021, a new scientific study was published that finally had an explanation for all these previous results, and provided a much more precise (though also complicated) explanation of how the A locus works in dogs.
In short, instead of just simple straightforward alleles caused by one mutation each, there are two „regions“ (promoters) of the ASIP gene that each have their variants, and the combination of those lead to several different phenotypes. One is the ventral promoter, which specifies how much red pigment is on the underside of the dog (how far up on the dog the red goes), and the other is the hair cycle promoter, which specifies if each hair should be all black, banded or only black tipped or even all red (very much simplified).
The study also found that the markers that were previously used for testing weren’t the causative mutations in most cases, which explains the false results. They also identified two new „tanpoint“ variants, and found that „saddleback“ is on ASIP itself and not on RALY after all. This, again, helps explain many previously questionable results.
We now have a new allelic series that reflects the new findings. The study used new terminology to set the new test apart from the old one. See the charts for more detail.
In short:
Old model: Ay > aw > at > a
New model (my suggestion): Ay > Ays > aws > aw > asa > at > a
New model (acc. to study / UC Davis): DY > SY > AG > BS > BB > a
It appears that zygosity plays an important role at this locus. Homozygous dogs are generally lighter than dogs that carry a more recessive allele. It has been shown in Shibas that Ays/Ays is lighter than Ays/at, for example.
WHAT DOES THAT MEAN FOR BREEDERS?
This new test allows for more accurate identification fo agouti vs. sable.
Some will find their dogs have a different genotype than what they previously believed or found via testing.
Those breeding for wolf sable should definitely consider using this new test on their breeding dogs to make sure they carry the desired aw allele.
TESTING AVAILABILITY
The new „ASIP haplotype“ test is currently available at UC Davis, and will soon be at Paw Print, VetGen, and Embark, from what these companies have mentioned on social media.
UC Davis A locus test: https://vgl.ucdavis.edu/test/agouti-dog
HOW TO VISUALLY TELL THE COLORS APART
(ee vs. Ay, Ays vs. aw)
While it is always best to DNA test breeding dogs, visual identification can be quite accurate if looking for some clues.
Those most easily confused are e/e (recessive yellow) and Ay (clear sable), as well as aw (agouti) and Ays (shaded sable).
The A locus colors also have quite some variation to them, also depending on if they carry recessives. The presence or absence of a dark facial mask (Em), the presence or absence of urajiro (countershading) and the shade of red can also influence how they look.
Some clues:
e/e dogs always have clear whiskers. They don’t have any black (or brown) hairs on the body (except a few stray ones due to somatic mutation). They often have a faded nose. They are born clear with no shading.
Ay dogs on the other hand are often darker as pups, with dark dorsal areas and often a dark muzzle. They may clear almost completely, but retain dark whiskers and often some dark hairs along the spine and on the tail gland.
aw dogs usually have dark hairs on their face including below the eyes, on the cheek and on top of the muzzle. They often have dark hairs down the legs. Ays dogs on the other hand will have much clearer faces as adults, though having a Em mask add black and complicate it. They will usually have clear legs (no black). As teenagers, both of these can go through very light phases and then darken again. Agoutis will usually end up with more dark on both body and face.
HOW TO BREED WOLF SABLE?
A wolf sable as required or aspired in Pomeranians has to be aw/- ky/ky E/- or Em/- and also i/i (low red intensity, governed by various loci).
aw can now be correctly tested for (presently at UC Davis).
The K and E locus are testable at many labs but are usually easy to deduce from parentage.
The most inclusive analysis for the intensity loci is available at Embark, while other labs offer a test for one of the involved loci.
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I hope the above information is helpful. I am happy to discuss the topic. Note that some of this is my own interpretation/suggestion (noted in the graphics accordingly).
