Page 78 - Aussie Magazine - 2024 Issue 3
P. 78
Informative
So what does this have to do with
protecting the genetic diversity of
all Merle breeds? The Mc allele is Before moving on I’d like to address the terminology of
the most common non-Expressing “Double Merle”. This is technically not a genetic term.
allele. As already mentioned the We would never say “Double Tan Points” or “Double
SINE insertion of Merle’s poly-A Black”. The terminology in the past has not only been
tail shortens more often to Mc used to describe a dog who is M/M - homozygous for M,
then to any other length and but more so refers to the white that can be created by
continues to shorten even from the combination of two Merle alleles and the possibilities
a length of Mc+. This has been of hearing and/or vision impairments. With the new
happening by way of mosaicism understanding of the alleles that are dependent upon the
since the Merle mutation first length of the poly-A tail of the SINE insertion, questions
occurred. We can presume that all have arisen as to what constitutes a “Double Merle”. Or
breeds who consistently breed for more so, which combinations of two Merle alleles can
the Merle trait have on average delete pigment to white and therefore come with the
38% of their phenotypically solid risk of hearing and/or vision impairments? Out of the 28
dogs having at least one Mc allele possible Merle allele combinations there are 14 that have
and a percentage having two. the ability to delete pigment to white. Here is the list all
We have always been breeding 14 grouped by the longest allele.
with Mc involved; we just did not
know it. The basic rule has been • Mc+/Ma+, Ma/Ma+, Ma+/Ma+
to breed “Merle x Solid” in order • Mc+/M, Ma/M, Ma+/M, M/M
to avoid any resulting “Double • m/Mh, Mc/Mh, Mc+/Mh, Ma/Mh, Ma+/Mh, M/Mh,
Merle” offspring, which for the Mh/Mh (the Mh allele can delete pigment even as
most part has served breeders heterozygous.)
fairly well over the years.
We need to start redefining what we refer to as a Double
There is however exceptions when Merle (DM). Mc/Mc+ is not a DM dog; Mc+/Ma is not a
a Merle x Solid breeding does not DM; Ma/Ma is not DM. And most importantly Mc/M is not
turn out as expected that I will Double Merle as no pigment will be deleted to white.
provide examples of later.
78 | A Worldwide Magazine for the Aussie • Issue 3/2024
