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Merle Color In Cocker Spaniels - Analyses Goal #1


Goal #1: Determine if scientific evidence can be provided to prove Merle is not a Cocker Spaniel color. If yes, provide such scientific evidence.


  • The gene mutation responsible for Merle patterning in dogs has been identified
  • The results of a study done at Texas A & M in 2006 were published in the Proceedings of the National Academy of Science (PNAS), a highly respected scientific journal
  • The PNAS paper is entitled: Retrotransposon insertion in SILV is responsible for Merle patterning of the domestic dog. L. A. Clark, J. M. Wahl, C. A. Rees, and K. E. Murphy. 2006 January 31; 103(5): 1376-1381
  • The study focused on six breeds: Collie, Border Collie, Australian Shepherd, Cardigan Welsh Corgi, Dachshund, and the Great Dane

Specific Findings of this Study

  • The SILV gene locus was chosen as a potential gene for Merle based upon the research that previously showed black hair color in mice dilutes with age. The SILV gene locus was investigated for any mutations in the Shetland sheepdog
  • A SINE, a short interspersed element, was found inserted in the SILV gene locus
  • This SINE insertion segregated with the Merle phenotype in multiple breeds and was absent from dog breeds that lack Merle patterning
  • The mutation was identical at the DNA level, (with the exception of two point mutations), in all breeds analyzed in this study
  • The SINE is a retrotransposon, and has a poly A tail. The cryptic mutation was found to have a longer poly A tail, the actual Merle mutation has a shorter poly A tail. During replication, the process can ‘fail’ and shorten the longer poly A tail in the cryptic mutation, and result in the shorter poly A tail. This then leads to the disruption of the SILV gene, and the manifestation of the Merle patterning

Discussion of the Findings of this study:

  • The SILV gene is expressed early in a developing embryo, and is within cells that become numerous different cells and tissues in the adult. Because of the widespread expression in different cells and tissues, this leads to the wide range of hearing and eye problems, as well as other organ systems defects such as the skeletal, cardiac, and reproductive systems
  • Finding the mutation was identical in each breed analyzed, and comparison of when each of the six different breeds historically emerged, the data indicates that the Merle mutation most likely existed prior to the establishment of different dog breeds. This means that it is likely that the predecessor to ALL dog breeds had the Merle mutation. The sequence data analysis was statistically significant
  • The normal function of the gene is unknown; the researchers hypothesize that it is involved in the biogenesis of pre-melanosomes, which differentiate and give rise to skin and eye tissue, and many different body tissues
  • The researchers applied for a patent for the Merle mutation

Implications & Conclusions for Cocker Spaniels

  • Based upon this significant research, the Merle gene mutation was present before dog breeds emerged. This would include the Cocker Spaniel
  • A DNA test is commercially available, as reported in the AKC Gazette article from August 2010 (IDEXX Reference Laboratories). The PNAS paper references a second company, Vita-tech, located in Canada
  • An ASC member obtained DNA samples of Merle Cocker Spaniels. The DNA results showed two were heterozygous Merles, one was a homozygous Merle. One can therefore conclude that the Merle mutation identified in the PNAS paper is the same mutation for Merle Cocker Spaniels
  • There have been individuals who have theorized that the Merle mutation was introduced into the Cocker Spaniel by a breeding with a Merle Australian Shepherd, that occurred in the 1980’s
  • We cannot scientifically conclude that the Merle gene was introduced by this breeding.
    • The statistically significant findings in the PNAS paper would indicate the mutation was present before individual dog breeds diverged
    • We do not have DNA samples from dogs from this reported breeding, nor do we have samples from the parents of this reported breeding. Without DNA samples, the testing cannot be performed
    • If the progeny of this breeding were then backcrossed with Cocker Spaniels, following 6 breedings or approximately 10 years, all progeny would test 99% pure Cocker Spaniel. i.e. If we could test every single Cocker Spaniel, even those with the Merle mutation, if they have only been bred with Cocker Spaniels, would test pure at the DNA level for Cocker Spaniel DNA
    • The AKC can identify all progeny down the multi-generational line back to these two parents. This confirms parentage but NOT carriers of the Merle mutation
  • For these reasons, proving the Merle gene was introduced by this breeding is not possible. Furthermore, there is no possibility of scientifically proving Merle color is not a Cocker Spaniel color

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