Home / Genetics / Merle Gene Explained
Merle is the pattern behind some of the most photographed dogs in the world: the marbled grey-blue coats of Australian Shepherds, the dappled Dachshund, the harlequin-adjacent Great Dane. It is also the coat pattern where genetics stops being a curiosity and becomes a welfare issue, because the same variant that paints the coat can, in double dose, damage hearing and vision. Our coat color genetics guide introduces merle as one switch among several. This page gives merle the full treatment it deserves.
The UC Davis Veterinary Genetics Laboratory describes merle as a SINE insertion in the PMEL17 gene, also known as SILV or Silver. A SINE is a short stretch of repetitive DNA that has copied itself into the gene. The insertion disrupts how pigment cells distribute dark pigment, so the coat grows in irregular patches: some areas fully pigmented, others diluted to grey, blue or pale brown. Two details from the laboratory's account matter for owners. First, merle dilutes only black-based pigment (eumelanin). A dog whose coat genetics produce no eumelanin in the hair, a yellow or red dog at the E locus, can carry merle invisibly. Second, inheritance is incompletely dominant: one copy usually shows the pattern, and two copies do not simply show it twice as strongly, they change the picture and the risk profile entirely.
Merle is not a tidy two-version gene. The insertion ends in a repetitive tail, and the tail's length varies. The UC Davis laboratory reports each allele as a measured size because size tracks the effect: short alleles, roughly the low 200s in its reporting, are cryptic merles that show little or no pattern; mid-range alleles produce the classic patchwork; the longest alleles produce extreme dilution toward white. The tail is also unstable across generations, so a parent's exact allele size does not guarantee a puppy's. For breeding decisions, though, the fine detail is secondary. What matters is the binary fact the laboratory's guidance keeps returning to: any merle allele, of any size, counts.
When two dogs that each carry a merle allele are bred together, each puppy has about a one in four chance of inheriting merle from both sides: a double merle. The UC Davis laboratory describes double merles as often mostly white, with a wide range of auditory and eye defects, and notes abnormalities of the skeletal, cardiac and reproductive systems are also reported. The mechanism is pigment biology, not bad luck: the pigment cells disrupted by two merle copies also do essential work in the inner ear and in the developing eye, so their failure shows up as deafness and malformed eyes rather than as coat color alone. Every double merle also passes a merle allele to all of its own puppies. For these reasons the laboratory states that breeding two merle dogs is discouraged, and responsible breed clubs treat merle-to-merle mating as prohibited. A single-merle parent bred to a DNA-confirmed non-merle partner cannot produce a double merle puppy. That one fact is the whole safety system.
Three traps catch breeders who work by eye. A cryptic merle looks non-merle because its allele is short. A red or yellow dog hides merle behind a coat with no dark pigment to dilute, the same masking our coat color guide explains at the E locus. And a dog with only a small merle patch, on an ear tip or a tail, is easy to register mentally as mostly solid. All three dogs can produce double merle puppies when paired with another carrier. The laboratory's recommendation follows directly: DNA test to establish merle status in any breed where the pattern occurs, before breeding, whatever the coat looks like. Buyers of puppies in merle breeds can ask the same question owners ask about hips or eyes: were both parents tested, and can I see the results?
A single merle pet needs nothing special beyond ordinary care; the pattern itself is not a disease. A double merle dog deserves two early checks: a hearing assessment (a BAER test gives a definite answer for each ear) and an eye examination, arranged through your veterinarian, so that training can be adapted from the start if hearing or vision is reduced. Deaf dogs thrive with visual and touch signals, and blind or partially sighted dogs map a home quickly; what they cannot do is compensate for an owner who never knew. If you adopt a mostly white puppy from a merle breed, ask about its parents and get those two checks done as a matter of routine. Breeding questions behind patterns like this one are covered more broadly in our dominant and recessive traits guide. Back to the genetics hub.
Merle is caused by an inserted stretch of repetitive DNA (a SINE insertion) in the PMEL17 gene, also called SILV or Silver, per the UC Davis Veterinary Genetics Laboratory. It dilutes patches of dark pigment, producing the mottled merle pattern. It acts only on black-based pigment, so a dog that makes no black pigment in its coat does not show the pattern even if it carries the variant.
A puppy that inherits a merle allele from both parents. Two merle carriers bred together produce, on average, about one double merle puppy in four. Double merles often have extensive white coats and a substantially higher risk of hearing and vision defects, and the UC Davis laboratory notes skeletal, cardiac and reproductive abnormalities are also reported. Breeding two merle carriers is discouraged for exactly this reason.
The merle insertion has a tail whose length varies. Short versions produce little or no visible pattern; dogs carrying them are called cryptic merles and can be misclassified as non-merle by eye. Merle can also be hidden by a red or yellow coat that shows no dark pigment. Both kinds of hidden carrier can produce double merle puppies if bred to another carrier, which is why DNA testing, not appearance, settles merle status.
A single merle copy is the normal genotype of healthy merle-patterned dogs in many breeds, and most live ordinary healthy lives. A small increased risk of hearing problems is reported even in single merles, far below the double merle risk. If your dog has one blue eye or patchy pigment, that is pattern, not illness. Mention any hearing concern to your veterinarian, who can arrange a hearing test.
The UC Davis laboratory reports the measured size of each merle allele rather than a simple yes or no, because size tracks with how strong the pattern is, from cryptic at the short end to the most dramatic dilution at the long end. Other laboratories group sizes into named categories. Either way, the breeding-relevant fact is whether any merle allele is present at all.
This page is general information drawn from the published guidance of the organizations listed under Sources below. It is not veterinary advice, and it does not replace your own veterinarian, who knows your dog. If your dog is ill, bleeding, struggling to breathe or has collapsed, contact your veterinarian or an emergency clinic straight away. For a suspected poisoning, the ASPCA Animal Poison Control Center is on (888) 426-4435 and the Pet Poison Helpline is on (855) 764-7661. A consultation fee may apply on the helplines.
Last updated: November 2026. How we work: our methodology.