There is actually no such thing as a blue merle
gene, perhaps that surprises you, even more of a surprise may be the
following truth...the Blue Merle Collie is in fact a TRICOLOUR!
All tricolours carry just two colour genes, both
for tricolour, otherwise they would not be tricolour, so the blue
merle carries two genes for colour and both these genes are
tricolour. However it has also inherited from one of its parents a
separate dilution factor, this dilution factor works on the black
diluting the pigment to produce the blue merle colour. The dilution
factor does not work to such effect over tan which is why the blue
merle animal generally maintains tan points.
1) what happens when we mate tricolour to blue
When we mate a Tricolour animal to a blue merle
animal, both will pass on a tricolour gene, remember they have no
other colour gene to pass on. If the blue merle parent does NOT also
pass on the dilution factor, the result will be a normal tricolour
puppy. If the blue merle parent DOES pass on the dilution factor,
the resulting puppy will be blue merle.
2) what happens when we mate two blue merles
When we mate TWO blue merles together, again both
animals MUST each pass on a tricolour gene resulting in a tricolour.
If neither merle parent passes on the dilution factor, this puppy
will remain a perfectly normal tricolour. Its genetic makeup will be
no different to that of a tricolour born of two sable parents!
If only one parent passes on the dilution factor
along with its obligatory tricolour gene, the result will be a Blue
However, if both parents pass on the dilution
factor the result will be a tricolour puppy in possession of TWO
dilution factors, and this puppy is referred to as a double dilute.
Because of the double dilution factor working on the pigment, the
puppy will be predominantly white, the eyes and ear canals will also
be affected, often resulting in blind and or deaf puppies, in
extreme cases the puppy will have no eyes at all. It will more than
likely also lack pigment around the eyes and lips, also the nose
will more often than not be predominantly pink.
These double dilutes, if mated to a tricolour,
would actually produce normal puppies, all of which would be blue
merle. It cannot produce tricolour puppies, for both sets of
tricolour genes carried by such an animal will also carry the
dilution factor, effectively rendering the dilute white animal a
dominant merle. However no one would advocate the keeping of such an
animal, for in most cases its enjoyment of life would definitely be
The safest way to produce the blue merle colour is
to always mate blue merle to tricolour, it is then totally
impossible to produce a defective dilute white.
Some misinformed people believe that by mating two
blue merle animals together, the chances of producing a higher
percentage of merles in the litter is increased, this is a fallacy.
Two blue merles mated together produce on average over several
litters 25% tricolour, 25% dilutes and 50% blue merle.
A Tricolour mated to a blue merle, again taking the
average over several litters, will produce 50% tricolour and 50%
blue merle, therefore the percentage of merle puppies is identical
but in the latter case, there are no defective white puppies.
Hopefully readers will appreciate the dilution
factor cannot be carried as a hidden recessive, If it is present
within the genetic makeup of any animal, that animal WILL BE MERLE.
We can therefor safely use the resulting tricolour progeny of our
blue merle parents in any breeding program, without fear of any
dilution factor cropping up in succeeding generations.
I should also like to end another myth. The colour
of the merle is NOT improved by mating two merles together, as
already explained, the blue merle colour is the result of a dilution
factor working on TRICOLOUR and double merle dilution results in
dilute white puppies and not a paler blue. The clarity of the colour
is dependant on the combination of two things. The strength of the
individual dilution factor, and the clarity of the black genes
carried by the two animals.