One of the arguments that is being used to “market” the blue merle cross breed corgis is that back in history when the Cardigans and Pembrokes were bred together, the Pembrokes carried the blue gene.
This fallacy is what has managed to perpetuate the fraud.
With the onset of DNA testing we have managed to unravel the mysteries of the genetics behind colour inheritance and now we know that the Blue Merle of the Cardigans is different than the “Blueys’ found in Pembroke Welsh Corgis.
First we need to understand the difference between Merle and Dilute.
Understanding Blue Merle
When the Merle gene is expressed it acts like bleach thrown on a piece of material. Random areas of colour will be wiped out with no set pattern to it, as seen in the Blue Merle Cardigan Welsh Corgi above.
In Merle dogs we see any amount of merling, from a tiny spot that can be difficult to detect, through to most of the body with only tiny flecks of the body colour. Since in Cardigans, breeders only breed merle to black and white, we see grey dogs with splotches of black. In other breeds, such as Australian Shepherd, red merles are allowed.
Since Merle (M) is a dominant Gene if a dog carries the Merle gene the merle pattern will be expressed. All merle dogs are genetically Mm. If they are not merle they are mm.
If we look at the result of breeding a Merle and non-merle parent in a Punnet square we get:
Half of the progeny will be merle, and half will not. Merles will never be bred together because at puppy that is homozygous for merle (MM) is at risk for health issues including deafness.
Understanding the Dilute Gene
In Pembrokes there is occassionally a puppy that appears to have gunmetal grey hairs, instead of black, as in the dog above. This is a result of a gene on the D locus. Unlike Merle which is dominant, the D gene is recessive and a dog needs to be “dd” in order to express dilution. In Cardigans the Dilute will result in chocolate or liver coloured puppies with usually brown noses.
In this case in order to express the gene both parents will need to be carriers, and even then only 25% of the progeny would be born showing dilute, 50% would be carriers, and 25% would be clear. Genetic testing now allows us to do breedings planned with eliminating recessives such as the dilute gene.
For more information and pictures of what “Blueys” look like in Pembrokes please see the linked webpages.
Pembroke Welsh Corgi Club of America – “Bluies”
Welsh Corgi-News – “Blue Corgis”
Dog Genetics – Introduction to Merle
So while there are “blue” Pembrokes they are a result of a totally different modifier than the one that causes the Blue Merle in Cardigans, and Pembrokes are never Blue MERLE.