What Is the Merle Gene?

The Merle gene affects pigmentation of coat, skin, and eyes. It produces a marbled coat pattern and is often associated with blue or bi-colored eyes.

Genetically, Merle is caused by a mutation in the PMEL17 gene (Silver locus) located on chromosome CFA10. This mutation dilutes eumelanin (black/brown pigment), while pheomelanin (red/yellow pigment) remains largely unaffected.

This genetic variation gives Merle dogs their distinctive appearance.

Merle and Animal Welfare Concerns

Under German animal welfare law (§11b TierSchG), breeding practices that knowingly produce offspring with suffering or health impairments are classified as “Qualzucht” (torture breeding).

Breeding two Merle carriers together is particularly critical, as it significantly increases the risk of severe congenital defects in offspring.

Health Risks in Double Merles

Dogs inheriting two copies of the Merle gene (homozygous, “Double Merle”) are at high risk for serious health problems, including:

• Congenital deafness

• Blindness

• Microphthalmia (abnormally small eyes)

• Colobomas (structural eye defects)

• Severe pigment deficiency

Reduced pigmentation in sensory organs is strongly associated with hearing and vision impairments.

The severity varies individually. Some Double Merles manage relatively well, while others suffer from additional complications such as heart defects or neurological disorders.

Because of their vulnerability, these dogs require:

• Consistent veterinary monitoring

• Structured environments

• Protection from UV exposure

• Specialized training approaches

Genetic Basics

Dominant Inheritance

The Merle gene is dominant. A heterozygous dog (single Merle) displays the typical coat pattern.

Homozygous Form (Double Merle)

When two Merle carriers are bred together, there is a statistical risk of producing Double Merle puppies, often with severe impairments.

Merle Allelic Variants

m (171 bp) - Wild type — No Merle pattern

Mc (200–230 bp) - Cryptic Merle — No visible Merle

Mc+ (231–246 bp) - Cryptic Merle plus — No visible Merle

Ma (247–254 bp) - Atypical Merle — Subtle lightening

Ma+ (255–264 bp) - Atypical Merle plus — Weak Merle pattern

M (265–268 bp) - Classic Merle — Standard Merle pattern

Mh (269–280 bp) - Harlequin Merle — Extensive dilution, often high white

• Coat pattern intensity

• Skin and eye pigmentation

• Risk of deafness and blindness

A high degree of white patterning, especially in Double Merles, correlates with increased sensory impairment risk.

Genetic testing is therefore essential in breeding planning.

Responsible Breeding Practices

Breeding with Merle is not inherently unethical.

However:

• Merle × Merle pairings must be avoided

• Merle × Non-Merle is considered safe

• Genetic testing should always be performed

• Inbreeding must be avoided

• Overall health must take priority over coat aesthetics

Any breeding practice with a high probability of producing impaired offspring is ethically unacceptable.

Breeds Commonly Carrying the Merle Gene

Merle appears in numerous breeds, including:

• Australian Shepherd

• Border Collie

• Shetland Sheepdog

• Cardigan Welsh Corgi

• Dachshund

• Great Dane

• Collie

• Miniature American Shepherd

• Catahoula Leopard Dog

• Chihuahua (controversial in some lines)

• Pomeranian (not recognized by all kennel clubs)

New crossbreeds and designer lines continue to emerge, making complete lists difficult.

Living with a Merle Dog

Single Merle dogs are usually healthy.
Double Merles often require specialized support.

Veterinary Care

• Annual eye and hearing examinations

• Increased monitoring for pigment-related skin sensitivity

• UV protection for light skin areas

• Early neurological assessment if indicated

Training and Communication for Sensory-Impaired Dogs

Dogs with visual or auditory impairments face unique challenges:

Orientation Challenges

• Increased insecurity

• Heightened startle responses

• Risk of social withdrawal or defensive behavior

• Training Approaches

Strengthen Remaining Senses

• Scent-based games

• Food-search tasks

• Tactile cue training

Tactile Communication

• Chest touch = “Stop”

• Hip touch = “Move forward”

• Harness cues for directional guidance

Vibration Cues

• Floor vibration

• Gentle leash signals

• Structured body positioning

Creativity, patience, and calm energy are essential.

Socialization

Controlled contact with calm, socially stable dogs helps:

• Reduce isolation

• Maintain social learning

• Improve confidence

Structured Environment

• Fixed routines

• Clearly structured home layout

• Safe retreat spaces

• Avoid frequent furniture changes

Predictability reduces stress.

Emotional Bond and Quality of Life

Merle dogs — especially those with impairments — rely heavily on stable human attachment.

Positive reinforcement is essential.
Punishment increases insecurity.

Regular rituals provide safety:

• Fixed feeding times

• Calm physical affection

• Predictable walk routines

Even dogs with impairments enjoy enrichment:

• Scent games

• Massage

• Safe garden exploration

With informed care, patience, and empathy, Merle dogs can live fulfilling lives.

The Dangerous Beauty of the Merle Gene

The aesthetic appeal of Merle coats must never outweigh animal welfare.

Double Merle breeding frequently leads to preventable suffering.

Anyone considering a Merle dog should:

• Choose transparent breeders

• Request genetic testing results

• Avoid Merle × Merle pairings

• Prioritize health over appearance

Beauty should never come at the cost of suffering.

Explore more research articles on dog behavior and training in our Research Library.

Explore more research articles on dog behavior and training in our Research Library.