Good Dog’s Policy on Merles

We established our Merle Policy to provide a framework for working towards population-wide improvements, which are a critical part of our mission.

by Dr. Judi Stella, PhD - Head of Standards & Research at Good Dog

What is a merle dog?

Merle refers to a color pattern found in a dog’s coat, caused by the merle gene. This unique pattern is typically made up of mottled, patchwork markings it causes in either a solid or piebald coat, showing up on coats that have black or brown as a base color. Merle coats come in a range of colors, including liver merle, red merle, and blue merle, with variations in patterns and patching. Some coats have equal patching, while others might have heavy patching with minimal merle visible in their coat. Merle dogs often have blue or odd-colored eyes and differing skin pigments.

However, the merle gene does not always result in the merle color pattern on a dog’s coat. Cryptic (also known as hidden or phantom) merles are dogs with the merle gene, but who have little or no merle coloring.

What is Good Dog’s policy on merles?

At this time, Good Dog accepts merles if the breed is one in which the merle gene is known to occur, the color pattern is a characteristic of the breed, or it is considered a breed standard color. Currently, the following are the only merle breeds accepted on Good Dog:

  • Alapaha Blue-Blood Bulldog
  • Australian Shepherd
  • Beauceron
  • Bergamasco Sheepdog
  • Border Collie
  • Cardigan Welsh Corgi
  • Catahoula Leopard Dog
  • Chihuahua
  • Cockapoo
  • Collie (Rough and Smooth)
  • Dachshund (Dapple)
  • Goldendoodle
  • Great Dane (Merle and Harlequin)
  • Hungarian Mudi
  • Miniature American Shepherd
  • Miniature Australian Shepherd
  • Norwegian Dunker
  • Old English Sheepdog
  • Old Time Scotch Collie
  • Pomeranian
  • Pyrenean Shepherd
  • Shetland Sheepdog

Why is Good Dog taking this approach?

We established our community standards to offer a framework for working towards population-wide improvements, which are a critical part of our mission.

The merle gene is associated with an increased risk for some serious health conditions, including, among others, deafness and blindness. Please see below for a discussion of the health risks associated with merles.

Currently, we recognize programs that breed merles in accordance with the breed standard. The breed standards provide guidance on how to decrease the risk of health problems when breeding merles, including rules regarding not breeding merles to merles and required health and DNA testing.

Due to the uncertainties surrounding the introduction of the merle gene into new breeds with the potential for an increased risk of problems, especially with the auditory (hearing) and ocular (vision) systems, we have made the decision to be cautious in our approach to ensure we are only promoting responsible practices. Accordingly, we have launched a program specifically to look further into the merle gene as we continue our efforts to conduct in-depth research and gather information from consultations with veterinary and scientific experts and the relevant scientific literature.

We note that our community standards, including our policy with respect to merles, are subject to continual revisions as new research becomes available.

What are the health risks with merles?

The reason we exclusively recognize programs that produce merles in the breeds listed above is because the merle gene is associated with an increased risk for some serious health conditions. These include anophthalmia (missing one or both eyes), microphthalmia (one or both eyes being abnormally small and malformed), deafness and blindness, and skin cancer. These health risks are more prevalent and severe in double merles (meaning dogs that have two copies of the merle gene) than heterozygous dogs (meaning dogs that have one copy of the gene).

As noted above, the merle gene does not always produce the merle color in the dog’s coat. This means there’s no way to know whether you’re breeding two merles together just by looking at the color of the dogs. The only way to be certain you are not breeding two merles together is to do a specific type of DNA test making successful breeding of healthy merles complicated.

Additionally, it is recommended that merles should not be bred into lines that carry piebald (white dogs with spots) or extreme white spotting patterns (dogs that are mostly white with minimal spotting). This is due to the fact that the incidence of hearing or vision problems in dogs increases when white markings cover the eyes and/or ears. Research is currently ongoing regarding the prevalence and severity of these problems in merles bred with dogs that carry piebald patterns.

Whether the presence of the merle gene results in the merle coloring and what the pattern looks like is influenced by the length of the “poly-A tail” that the merle gene has. It is recommended that, in addition to DNA testing, breeders also test for tail length. Currently, this test is only available at a small number of laboratories.

This color pattern recently emerged in several breeds where it previously hadn't occurred. The odds of this mutation spontaneously appearing in multiple breeds in the last few years is unlikely. More likely is that the gene was introduced into new breeds. The introduction of the merle gene into a new breed has the potential of introducing health problems into a breed where they did not previously exist, the implications of which are often not adequately known or communicated to the public.

These issues are exacerbated by the fact that merles outside of the accepted merle breeds are sometimes marketed as a “rare” color and sold by breeders whose primary criteria is to breed for color ahead of other more important considerations such as health, structure, and temperament. If you are still considering buying or breeding a merle outside of the accepted merle breeds, we encourage you to reach out to us for more information at screening@gooddog.com.

Feedback

Our community is founded on a commitment to listen, learn, and as with so many issues in the dog world, sometimes people have very different opinions and it can take time for us to determine what makes sense for our community. If you disagree with anything about our approach or have any questions or feedback for us, please feel free to contact us anytime at feedback@gooddog.com.

Thank you so much for your time.

Reference & further reading

Ballif B, C, Ramirez C, J, Carl C, R, Sundin K, Krug M, Zahand A, Shaffer L, G, Flores-Smith H. The PMEL Gene and Merle in the Domestic Dog: A Continuum of Insertion Lengths Leads to a Spectrum of Coat Color Variations in Australian Shepherds and Related Breeds. Cytogenet Genome Res 2018;156:22-34. https://www.karger.com/Article/Pdf/491408

Clark LA, JM Wahl, CA Rees, KE Murphy. Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog. Proceedings of the National Academy of Sciences Jan 2006, 103 (5) 1376-1381. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1360527/pdf/pnas-0506940103.pdf

Langevin M, H Synkova, T Jancuskova, S Pekova. Merle phenotypes in dogs - SILV SINE insertions from Mc to Mh. PLoS One. 2018;13(9):e0198536. Published 2018 Sep 20. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6147463/pdf/pone.0198536.pdf

Murphy, S and Clark, LA. The genetics of merle coat patterns in dogs. 2018. https://blogs.biomedcentral.com/on-biology/2018/08/03/the-genetics-of-merle-coat-patterns-in-dogs/

Murphy SC, Evans JM, Tsai KL, Clark, LA. Length variations within the Merle retrotransposon of canine PMEL: Correlating genotype with phenotype. Mobile DNA. 2018, 9:26. https://mobilednajournal.biomedcentral.com/track/pdf/10.1186/s13100-018-0131-6

Pelles Z, A Gáspárdy, L Zöldág, X Lénárt, N Ninausz, L Varga, P Zenke. Merle allele variations in the Mudi dog breed and their effects on phenotypes. Acta Veterinaria Hungarica. 2019, 67:2, 159-173 https://akademiai.com/doi/pdf/10.1556/004.2019.018

Strain, G. Hereditary Deafness in Dogs and Cats: Causes, Prevalence, and Current Research. https://www.vin.com/apputil/content/defaultadv1.aspx?pId=11165&id=3848661

UC Davis Veterinary Genetics Laboratory https://www.vgl.ucdavis.edu/services/dog/Merle.php