What a coat-colour panel actually tells you
A coat-colour certificate reads like a health document and isn't one — with one exception that genuinely is.
A litter advertised with a DNA colour certificate looks like it has been thoroughly checked over. Mostly, it has been checked for one thing: colour. This is the companion piece to what a DNA health panel actually tests for — a standard coat-colour panel says nothing about hips, elbows, eyes or any inherited disease, with a single, important exception that sits inside the colour test itself and has nothing to do with how the puppy looks.
What's actually on the panel
A typical commercial coat-colour panel tests somewhere between five and seven loci, each one a specific, named gene rather than a general "colour test". A representative UK panel — Laboklin's seven-test bundle, at £138 including VAT — covers the A-locus (Agouti, which governs sable, tan-point and recessive black patterns), the B-locus (brown dilution, giving liver or chocolate), the D1-locus (dilution to grey/blue or lilac/isabella), the E1-locus (red, yellow, cream and apricot pigment), the I-locus (intensity of red pigment), the K-locus (solid colour versus agouti patterning, with brindle tested separately) and the S-locus (white spotting). A handful of breeds need extras the standard panel doesn't cover — Australian Shepherds and Lancashire Heelers need rare B-locus variants, French Bulldogs need a separate Cocoa test, and several breeds including Chow Chows, Chihuahuas and Hungarian Pumis need additional D-locus variants the base panel misses.
None of that is a health claim. The Kennel Club records D-locus results as part of its DNA testing scheme for Labradors specifically, because dilute colour in that breed has a known cosmetic paper trail worth tracking — but dilution itself, so far as the genetics are currently understood, is just a colour. It isn't linked to any disease. The one dilution-adjacent condition breeders do watch for, colour dilution alopecia, has no DNA test at all yet, and the working advice is simply to pair healthy dilute dogs with other healthy dilute dogs rather than to screen it out at the genetic level.
The one line on the panel that isn't about colour
Merle is where a coat-colour test stops being purely cosmetic. The pattern comes from an insertion in the PMEL17 gene, and a dog carries zero, one or two copies of it. One copy (heterozygous, sometimes written Mm) produces the mottled merle pattern breed standards describe in Australian Shepherds, Collies, Dachshunds, Great Danes, Cardigan Welsh Corgis and a dozen other breeds, and on its own carries a modest, well-documented risk: fewer than 1% of single-merle dogs are deaf in both ears.
Two copies — a double merle, produced whenever two merle dogs are paired — is a different matter. Double merles typically carry far more white in the coat and a much smaller area of pigment, and the same mechanism that produces the colour appears to disrupt development in the inner ear and the eye. Reported rates of bilateral deafness in double merles run from around 10% in Catahoula Leopard Dogs to roughly 56% in Australian Shepherds and as high as 85% in some of the other breeds studied. Eye defects — undersized, sometimes non-functional eyes, abnormal pupils — are common alongside the hearing loss, and some double merles also show skeletal, cardiac or reproductive abnormalities. Every double merle, regardless of whether it shows any of these effects itself, passes a merle allele to all of its own offspring.
The complication breeders can't see their way around by eye: merle doesn't always look like merle. A cryptic merle carries the gene but shows the pattern only in a very small patch, or not visibly at all. A hidden merle can carry it behind a red or cream (e/e) coat that masks dark pigment altogether, pattern included. Both can be paired with another merle dog by a breeder working from appearance alone, with the same double-merle risk as a visibly obvious pairing. The allele's insertion length can also shift slightly between a parent and its offspring, so even a known merle parent's result isn't a guarantee of what a puppy will test as. None of this is visible from a photograph, and very little of it is visible from the dog in front of you.
What to actually ask
For any breed where merle appears in the standard — or where a cross has introduced it — ask whether both parents have been DNA tested for merle specifically, not just colour-typed by eye, and ask to see the result rather than take the coat as the answer. A single merle parent paired with a confirmed non-merle partner is the only pairing that avoids the double-merle risk outright. Two merle-patterned parents, or one visibly merle parent and one of unknown status, is the pairing worth asking harder questions about before it goes ahead — on average a quarter of that litter will be double merle, whatever the parents' own hearing and eyesight suggest about the risk.
For every other line on a colour certificate — agouti, brown, dilution, intensity, spotting — the honest answer is that it tells a buyer what the puppy will look like, and nothing about its health. That's a reasonable thing to want to know. It just isn't the same question as a health panel, and a certificate that answers one is easy to mistake for an answer to the other.
Sources
- Merle — Veterinary Genetics Laboratory, UC Davis
- What Makes the Merle in Dog Coats? — American Kennel Club
- Coat Colours / Length — Laboklin UK
- Dog Coat Color and Type — Veterinary Genetics Laboratory, UC Davis
— Rene
Pieces along the same line
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The GenoVaq journal publishes long-form pieces for breeders and buyers — welfare, health-testing, breeding decisions, marketplace mechanics. New writing every week or two.