Merle and Brindle Dogs: Colour Genetics and Health

What is a merle dog?

A merle dog has patches of diluted colour scattered among patches of full colour. On a black dog the diluted parts look silvery blue-grey, which is blue merle; on a red dog the same pattern is red merle. The Dogs Australia Shetland Sheepdog and Rough Collie standards describe blue merle as clear silvery blue, splashed and marbled with black. Eyes are often blue or part blue: both standards allow one or both eyes to be blue or blue flecked in merles.

The gene was found in 2006. Researchers at Texas A&M University reported in PNAS that merle is caused by a small piece of inserted DNA (a SINE insertion) in a pigment gene called SILV, now usually called PMEL. They described merle as inherited in an incompletely dominant way, which means one copy shows the pattern and two copies show a stronger effect. The same paper noted that dogs with one or two copies can show a range of hearing and eye abnormalities, which is why the number of copies matters so much.

Two details worth knowing before you fall for a merle puppy. Merle coats change: the Australian Shepherd standard says merles characteristically become darker with age. And merle only dilutes the black or brown pigment, so on a mostly red or cream dog it can be hard or impossible to see, which matters for breeding (below).

What is a double merle, and why is it a health risk?

A double merle inherits the merle gene from both parents. The Louisiana State University veterinary school explains that when two single merles are bred, about 25% of puppies will be double merles, and that these dogs usually have a solid white coat and blue eyes, are often deaf and/or blind, and may be sterile. Its advice is blunt: breeders in these breeds know not to breed merle to merle.

The hearing figures come from a 2009 study of 153 merle dogs of several breeds, each hearing tested with a BAER (brainstem auditory evoked response) test and DNA tested for merle.

Strain et al., Journal of Veterinary Internal Medicine (2009), led from the Louisiana State University School of Veterinary Medicine. The study found no significant link between deafness and eye colour or sex. Study figures, not a prediction for any one dog.

Eyes are the other half of the problem. In a 1978 study of 44 Dachshunds bred to investigate the merle gene, all 11 extreme dapples (double merles) had severe eye defects in variable forms, including small eyes (microphthalmia), small corneas, misplaced pupils, cataracts and colobomas (gaps in eye structures). Single merles showed milder changes, and the solid-coloured control dogs showed almost none of them. Not every double merle is deaf or blind, but no responsible breeder takes the chance.

What is a cryptic or hidden merle?

A merle you cannot see. Later research found merle is not one variant but a range. A 2018 study of 175 Australian Shepherds and related breeds measured the length of the merle insertion and found it varies continuously, with at least four major groups it called cryptic, atypical, classic and harlequin merle. The short “cryptic” versions often behave like no merle at all. A 2018 PLoS ONE study described six merle alleles, each linked to different coat features and different health risk, and found mosaic dogs carrying more than one version in 16.6% of its 181 dogs.

The other way merle hides is under a red coat. Because merle dilutes black and brown pigment, a red or cream dog can carry full merle and show little or none. A 2021 study of 140 Dachshunds found many such hidden merles, and one dog with no visible merle that produced a double merle puppy born without eyes. A 2019 study of the Mudi made the same point: hidden merles can unintentionally produce double merle puppies with eye, hearing and survival problems.

What makes a dog brindle?

Brindle is dark stripes over a red, fawn or golden base. The Dogs Australia Boxer standard puts it as black stripes on a golden-yellow or red-brown background, and the French Bulldog standard as a mixture of black hairs and fawn hairs.

The gene is different from merle. A 2007 study in Genetics, using a Labrador and Greyhound cross, mapped a gene called the K locus and found three versions with a dominance order: dominant black, then brindle, then the version that lets yellow, fawn and red show. A companion paper in Science the same year identified the K locus as beta-defensin 103 (CBD103). In plain terms, a dog with the brindle version shows stripes wherever its coat would otherwise be red or fawn, and a dog with dominant black hides brindle altogether.

Brindle carries no known health risk of its own. None of the brindle genetics studies cited here links the pattern to deafness, eye defects or any disease, and it is a standard colour in breeds as different as the Greyhound and the Boxer. A brindle dog's health is about its breed or mix, not its stripes. That is the big difference from merle.

Which breeds come in merle or brindle?

Here is what the Dogs Australia breed standards say for breeds you are likely to meet in Australia, with links to the rescue listings for each.

Dogs Australia breed standards, read 9 and 10 November 2026; the Koolie row is from the Koolie Club of Australia because the Koolie has no Dogs Australia standard page. “Not listed” means the standard does not name the colour; “Allowed” means it falls under “any colour”.

Two breeds need a note. Dachshund dapple is merle by another name, and the Dogs Australia standard lists double dapple, with white all over the body as well as dapple, as unacceptable in any variety. The Great Dane harlequin, white with torn-looking black patches, is merle plus a second gene: a 2011 Genomics study found harlequin needs one copy of the merle insertion and a mutation in a gene called PSMB7, and that two copies of the harlequin gene are lethal before birth.

The Australian Cattle Dog is often called blue, but its coat is speckle, not merle. Our blue heeler vs red heeler guide explains the difference.

Is merle allowed in Australia, and how do you spot a bad merle breeder?

Merle is allowed in the breeds whose standards include it. Breeding two merles together is not. Dogs Australia's registration regulations (regulation 6.3.4.2) have prohibited merle to merle and dapple to dapple matings since 1 January 2015, stating that the merle or dapple gene carries an increased risk of impaired hearing and sight problems. Puppies from such a mating can only go on the Limited Register, endorsed never to be upgraded, and a breach is an offence by the owners of the sire and dam. In a Dogs Australia buying guide, the chair of its Canine Health and Wellbeing Committee says merle should never be doubled up because it causes deafness and blindness.

Merle has also been pushed into breeds that never had it. The same Dogs Australia guide says merle does not occur naturally in the French Bulldog and that dogs bred “just for colour” are not purebred French Bulldogs, and since 1 July 2025 the regulations allow merle French Bulldogs (and merle Chihuahuas) on the Limited Register only, never to be upgraded, once DNA has confirmed breed purity and parentage. The Chihuahua, Pomeranian, Whippet and Shih Tzu standards rule merle out.

Warning signs when a seller is advertising merle puppies:

• Both parents are merle. Sometimes offered as a selling point. It is the one pairing Dogs Australia bans, and about a quarter of the puppies would be double merles.
• A mostly white puppy with blue eyes from merle parents. That is the double merle look the Louisiana State University vet school describes. Ask for hearing and eye checks before anything else.
• “The other parent is solid” with no DNA test, in a merle breed. Cryptic and hidden merles look solid. Ask for the merle DNA result.
• Merle in a breed whose standard excludes it, such as a merle French Bulldog, Chihuahua or Pomeranian, sold as “rare” at a premium.
• Pressure to pay a deposit before you see the puppy with its mother. Scamwatch warns that scammers advertise pets that do not exist; meet the pet in person or by video call with the breeder, and check the breeder is legitimate and accredited.

For the state breeder numbers and the full scam checklist, see puppies for sale: adopt or buy?. Breed-specific guides cover the Australian Shepherd, Dachshund, French Bulldog, Chihuahua and Great Dane.

Should you adopt a double merle?

If you can give a deaf or low-vision dog the setup it needs, yes. Double merles do turn up in Australian rescue listings now and then. Rescues usually note on the listing whether a dog is deaf, partly deaf or has limited sight, and a foster carer can tell you how the dog copes day to day.

What living with a deaf dog involves, from SPCA New Zealand's advice:

• Hand signals. Pick clear, distinct gestures for cues like sit, stay and come, and use them consistently. The Louisiana State University vet school publishes a set of hand commands, several borrowed from sign language.
• No startling. Gently tap the floor near a sleeping deaf dog, wave a hand in its line of sight or lightly touch its shoulder.
• Secure fencing, and off-lead only in safely enclosed areas. In public, use a lead or long line.
• No shock collars. SPCA New Zealand warns they can be distressing and may damage your relationship with your dog, and recommends reward-based training.

Low vision needs a predictable home: furniture that stays put, gates at stairs and a calm introduction to new places. Ask your vet to examine the eyes and hearing soon after adoption, and ask the rescue what checks have already been done. A single merle needs no special setup at all, and the Koolie Club of Australia says the way breeders avoid double merles is to breed a merle to a solid-coloured dog.

Weighing up a dog with extra needs? The adoption readiness check takes a few minutes, and our guide to adopting a dog in Australia covers the steps from application to home.

Find a merle or brindle dog near you

Rescues list by breed, so here are the breeds most likely to carry each pattern, by city:

Every listing links to the rescue, where you apply directly. Not sure which breed suits you? Try the what dog breed am I quiz, and if your rescue dog's coat has you guessing at its mix, see what breed is my rescue dog?.