Colour genetics puzzle

The tested genotypes have been given.
Everybody realized, that these result in offspring with black base color.

Since both parents have Irish spotting pattern, this is expected to show in the offspring as well.

Would either parent carry piebald, it would show as a pseudo-irish pattern, which wasn´t the case.

Is there a possibility for brindle offspring? No, because brindle dogs jave the genotype KB/ky on the K-locus (which wasn´t the case for both parents).

But something very important hasn´t been tested: The M-locus!

Both parents have a base color, on which merle shows little or not at all. If you have a close look, you can see small blue speckles in the parent´s eyes (very tiny, I admit). There are also some greyish strands in the shoulder area of the male parent. All these hints are very discrete and can bee missed easily – as in a “real” sable merles.

Both dogs in my example are Mh/m – which makes this a high risk mating.

Each puppy has a 25% risk for the genotype Mh/Mh, which in turn has a high risk for visual and auditory impairment.

This is why dogs with unknown merle genotypes should never be mated in breeds or populations with merle, if merle alleles with higher insertions (e.g. M or Mh) can´t be excluded.

All puppies of this mating have a 50% chance for the genotype Mh/m, which can express in very different ways. For example as minimal merle (shown in the chart as the dog below). Here is just a very small merled area (if not overlayed by a white marking).

With this riddle and its resolution I would like to sensitize fort he risks of merle breeding, because merle is high fashionable and bred for in much more breeds than the few breeds formerly known as traditional merle breeds.