Page 127 - Aussie Magazine no1, 2023
P. 127
The Tweed phenotype
is described as a Merle
pattern that expresses with
random shaded-in or solid
areas, usually with two or three
distinguishable shades. Once
thought to be a modifier of Merle
and now shown to be created by
several different Merle genotypes.
abnormalities together with
very pale or completely
white coat phenotypes
(Strain et al. 2009). Such
negative health effects
associated with the M locus encouraged the head, body and tail (poly-A tail) which contains a
research to identify the gene responsible. long string of repeating base pairs. This mutation
impairs the ability of cells to produce normal
If you have been breeding Aussies for any length pigment and leaves random areas of the coat
of time, it is likely that at some point your dam which are diluted to a lighter pigment. When Dr LA
has whelped a pup which has left you mystified Clark identified the Merle mutation in 2006 it was
by what you were seeing. Perhaps white body an exciting time! We thought we would get the
splashes that were not expected and are not to answers we were searching for that had eluded
standard; dilute looking pups when d/d is not a breeders for generations. What came next was
possibility; brownish or off-shading on a black disappointing to say the least - solid dogs testing
offspring; excessive white offspring and yet one as M/M that did not produce Merle offspring.
parent is phenotypically solid; Merle offspring How could that be? It left so many questions
that were not expected as neither of the parents unanswered that the testing was considered by
express a Merle pattern; a solid pup when one many to be flawed and in 2009 the only lab testing
parent is M/M and all pups should be Merle; an for Merle under patent removed the test from their
unusual Tweed Merle pattern unlike that of the colour panel.
Merle parent and other littermates. The Tweed
phenotype is described as a Merle pattern that In 2010 Thermo Fisher introduced the ABI
expresses with random shaded-in or solid areas, 3500 Genetic Analyser. We didn’t realise it
usually with two or three distinguishable shades. at the time but this advanced analyser would
Once thought to be a modifier of Merle and now give us the answers we had been searching
shown to be created by several different Merle for and give breeders the information
genotypes. needed to make educated breeding choices.
The original Merle test could only accurately
There have always been questions surrounding identify the body of the Merle mutation and the
Merle - a SINE insertion consisting of 3 parts - assumption was made that any reasonable length
A Worldwide Magazine for the Aussie • Issue 1/2023 | 127
