December 14, 2017

Coat Color in Dogs

Identification of the Merle Locus in the Australian Shepherd Breed

The merle phenotype was studied to uncover genes and mechanisms involved in the complex pathways of pigmentation.

For this experiment, no dogs were housed. All were independently owned pets. Data on blood, pedigrees and the coat colour were collected by DVM veterinarians. Using a BACC 3 kit, genomic DNA was extracted. Pedigrees were then constructed and used for genetic linkage analysis.

Knowing that the merle phenotype was determined by genetics, researchers went out to determine where the genes were located.  They believed that three genes played massive roles in the merle phenotype: MITF, PAX3 and SOX 10. However, the genetic linkage study disproved this belief. They used a pedigree of 96 Australian Shepherd dogs and utilized a genetic linkage approach to determine the location of the locus in which the gene should reside, and with high statistical support they found the locus where the gene that plays a role in the merle phenotype should be located. They analyzed a sub pedigree with a focus on the SOX 10 gene to determine where the merle locus was, and the genetic linkage analysis confirmed the location.

The gene MITF is excluded from the merle phenotype, but it is believed that the merle mutation affects a gene that interacts with the MITF gene. Additionally, while they believe that hearing loss might be attributed to the white phenotype, they don’t know if microphthalmia and other ocular issued is caused by the white phenotype, though it may lie on the same locus.

“This locus is at the centromeric end of CFA10 and spans 5.5 Mb and is linked to the merle coat colour with a maximum Lod score of 19.87 and a recombination fraction of 0.”

Two-point linkage analysis in three other breeds allowed the researchers to conclude that they had in fact fount the location of the merle phenotype.

Hédan, B., Corre, S., Hitte, C., Dréano, S., Vilboux, T., Derrien, T., Denis, B., Galibert, F., Galibert, M. and André, C. (2006). BMC Veterinary Research, 2(1), p.9.

Reviewed by: Anneliese Ceisel