Page 126 - Aussie Magazine no1, 2023

Informative

It has been recognised that the Merle coat pattern which was identified in 30 out of 181 (16.6%)
in dogs is not only a visually interesting feature, dogs in our study group. Importantly, not only
but it also exerts an important biological role, in major alleles, but also minor Merle alleles can be
terms of hearing and vision impairments. In 2006, inherited by the offspring. Thus, mosaic findings
the Merle (M) locus was mapped to the SILV gene cannot be neglected and must be reported to the
(aka PMEL) with a SINE element in it, and the breeder in their whole extent. Most importantly,
inserted retro element was proven causative to sperm cells seem to be a significant source of
the Merle phenotype. Mapping of the M locus germline Merle allelic variants which can be
was a genetic breakthrough and many breeders passed to the offspring on Mendelian basis and
started implementing SILV SINE testing in their explain unusual genotype / phenotype findings
breeding programs. Unfortunately, the situation in the offspring. In light of negative health
turned out complicated as genotypes of Merle consequences that may be attributed to certain
tested individuals did not always correspond Merle breeding strategies, we strongly advocate
to expected phenotypes, sometimes with implementation of the refined Merle allele testing
undesired health consequences in the offspring. for all dogs of Merle breeds to help the breeders
Two variants of SILV SINE, allelic to the wild in selection of suitable mating partners and
type sequence, have been described so far–Mc production of healthy offspring.
and M. Here we report a significantly larger
portfolio of existing Merle alleles (Mc, Mc+, Ma, The Merle pattern can be seen in various breeds, Text written by: Mary Langevin & team. Photographs provided by: Martina Svecova
Ma+, M, Mh) in Merle dogs, which are associated such as the Australian Shepherd Dog, Australian
with unique coat colour features and stratified Koolie, Border Collie, Dachshund, French Bulldog,
health impairment risk. The refinement of allelic Louisiana Catahoula, Labradoodle, Miniature
identification was made possible by systematic, American Shepherd, Miniature Australian
detailed observation of Merle phenotypes in a Shepherd, Pyrenean Shepherd, Rough Collie,
cohort of 181 dogs from known Merle breeds, Shetland Sheepdog, Welsh Sheepdog, Cardigan
by many breeders worldwide, and the use of Welsh Corgi, Chihuahua, Great Dane etc. Merle
advanced molecular technology enabling the is thought to be inherited in an autosomal,
discrimination of individual Merle alleles with incomplete dominant way. Dogs heterozygous for
significantly higher precision than previously the M allele show a typical coat pattern, however,
available. We also show that mosaicism of Merle dogs homozygous for the M allele may also exhibit
alleles is an unexpectedly frequent phenomenon, auditory and ophthalmologic impairments and

126 | A Worldwide Magazine for the Aussie • Issue 1/2023