What causes a deafness and blindness in dogs?

Have you hear of the term Merle? In what context have you heard the term used? Over the course of the next few Thursdays, I will share with you some research I have done on Merle's to help our understanding with what Might be going on with Mango. By the way, Mango is still up for adoption through Pet Rescue By Judy.

Pet owners familiar with the term Merle, often know of it as in the colour of a dog's coat. Here is a photo of Linus.... you may describe him as a Merle Blue.



Well, here is something you may not know. I did not, and was introduced to it by one of Doglando's Dads. We were asking him about Mango, and for his opinion on what caused Mango to be deaf and blind. His first answer to us was "I am not a veterinarian..." (he is a Cardiologist) and then he proceeded to educated us about the Merle gene.

There is no such thing as a sable merle gene, or red or blue merle gene...there is only a merle gene. Merle is an incomplete dominate gene, which means this gene will show up in offspring.

Merle is a dilution gene. That means, the merle gene will lighten up whatever colour a dog's coat would otherwise have...thus the spotted, patchy, salt and pepperish look. The lightening is not spread evenly all over the coat, but rather the merle gene does not allow certain parts of the dogs' coat to pick up other colour, therefore leaving undiluted colour scattered all over the dog's body.

Merle seems to work primarily on the black and brown colour of the dog's body, leaving any light or tan coloured spots alone.

Doggy colour palette:

One merle gene on an otherwise black dog, produces a blue merle...

Merle does not get rid off or eliminate the tan on a dog's coat, so in a tricolour dog, the tan points on his/her ears, eyes, muzzle and legs will still be present on a merle dog. If the tan will not be present on a black dog, it will not be present in the merle dog either...

One merle gene on an otherwise sable dog, produces a sable merle...

Merle acts on the dark pigmentation in the iris of the eye, just as it does on the coat, which is why merle dogs often have white in their eye or blue eyes.

Here is a photo to describe the above:


Basic Genetics:

We know we have to have two copies of a gene, alike or different to form correct? So, lets call the Merle gene M and the non-merle gene m. The different combinations we can have are as follows:
MM, Mm or mm correct?

So based on the above, it would mean that the MM dog has two Merle genes, the Mm dog has one Merle and one non-merle gene, and the mm dog has two non-merle genes.

The MM dog is referred to as a double merle more commonly known as a Homozygous Merle.
The Mm dog will dog would be referred to as a blue merle or sable merle (for the sakes of discussion). Had this dog not had the one M gene, he/she would have been a solid colour.
The mm dog is the "normal" coloured dog: full colour, tri colour, sable, liver etc.

So what does this have to do with blindness and deafness in dogs?
Double Merle pups (MM) are born to parents that are both Merle. It does not matter how much merle or how little merle either of the parents have, research shows 25% of their litter will be double merle (http://www.lethalwhites.com/doublemerle.html).

Not always, but very often, double merles are born deaf or blind and sometimes both; and may have other physical problems.

It is important to know that Merle is not a colour, it is a pattern. Until next time, absorb how a dog's pain palette is created and we will pick up from here.

Dog Responsibly....University of Doglando