What is merle genetic testing?

Merle colouration is caused by a variant in the PMEL gene. The type of variant varies between dogs and determines both the degree of visible merle pattern and the risks associated with breeding. Standard genetic testing identifies the variant type and assigns a classification such as m, Mc, Mc+, Ma, Ma+, M or Mh. Please note that every dog will carry two variants since they will inherit one variant from each parent and therefore the test results received will identify both variants that the dog has inherited. For example, the test results for a dog whose mother has passed the m variant on and whose father has passed on the Mc variant will be recorded as m/Mc.

A visibly merle dog will always have at least one merle variant. If genetic testing reveals no merle variants are present, then your dog is not merle – some colourations can be similar to merle and cause dogs to be mistakenly described as being merle when they are not. If your dog’s genetic test results do not show any merle variants but you still believe your dog does have merle colouration, then you should consider re-testing your dog or consulting your test provider to query the results.

Testing requires a DNA sample, typically a cheek swab sample. Swab collection kits can be obtained directly from the testing laboratory. Results are typically returned within two to four weeks.  

Laboratories

The following laboratories are currently able to carry out merle genetic testing which distinguishes different merle variants. Results from laboratories marked * are also recognised by the Royal Kennel Club and recorded in their database for RKC registered dogs.

  • Genomia (Czech Republic) *

  • UC Davis (USA) *

  • Orivet (Australia) *

  • Laboklin (Germany) *

  • Tilia (Czech Republic)

  • EVG (Slovenia)

  • InfogeneNZ (New Zealand)

  • UML (South Africa)

  • Feragen (Austria)

The IHA does not require testing to be carried out at an RKC-recognised laboratory. All laboratories listed above are considered appropriate for the purposes of this assessment. Please note that some laboratories who advertise genetic testing services do not conform with the current best practice for these types of genetic tests and are therefore excluded from the list above. The list shown above identifies laboratories that carry out the current recommended form of testing.  

Understanding the test classifications

Laboratories typically report one of the following results:

  • m — no merle variant present

  • Mc — very short cryptic variant (up to 230 bp): generally no visible merle pattern

  • Mc+ — short cryptic variant (231–246 bp): may show minimal merle pattern

  • Ma — shorter merle variant (247–254 bp)

  • Ma+ — shorter merle variant (255–264 bp)

  • M — classic merle variant (265–269 bp)

  • Mh — longer merle variant (270 bp or greater)

Where a dog has multiple variant lengths (mosaicism), breeding decisions should be based on the longest variant identified.

As noted above, every dog will have two variants since they inherit one from each parent, so the genetic testing results will show both inherited variants.  

Summary of compatible pairings

The following summarises which mating partners are considered compatible based on the test result for the longest merle variant identified in a visibly merle dog.

No merle variant (m)

Outcome: PASS

The dog may be bred with any mating partner. No breeding restrictions apply under this criterion.

————

Shorter merle variants (Mc, Mc+, Ma, Ma+, M – under 270 bp)

Outcome: CONDITIONAL PASS

The mating partner must also be genetically tested and confirmed as either:

  • having no merle variant (mm); or

  • having a very short merle variant only (Mc – 230 bp or less).

————

Longer merle variant (Mh – 270 bp or greater)

Outcome: CONDITIONAL PASS

The mating partner must also be genetically tested and confirmed as:

  • having no merle variant (mm) only.