Ultimo aggiornamento:  04.11.2019 16.11
October 13, 2008

Blue Merle Genetics in Simple Terms

By  Angela Harvey


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 merle?

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 together?

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 merle puppy.

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 impaired.

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.