Merle gene

[cassie]

Are there any geneticists here? I have some questions about the merle gene, and I am not really sure where to go for answers. In my college genetics class, I was told that it was a lethal gene and that animals that were homozygous for the trait died in utero and were never born at all. I have since learned that is not necessarily true. Double merles can be born but they may have serious birth defects such as blindness or deafness or both. What I want to know is why. How does the gene cause all these problems? Is there a good book that would address this?

 

[oldhenlikesdogs]

https://www.akc.org/expert-advice/dog-breeding/merle-in-dogs/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7349775/

There are a lot of sites that discuss the merle gene. Some is more technical than others. Having been an Australian shepherd owner myself for many years I have read a bit about it. You can probably find some basic information on most breed books where merle is a regular color.

Despite all the recent claims of merle being a dormant gene in many breeds and that it just shows up one day that is all incorrect.

Breeders need to be careful as there is something called a cryptic merle where you can't always tell if a dog is actually merle.

 

[oldhenlikesdogs]

https://www.ashgi.org/home-page/genetics-info/color/merle-health

https://www.ashgi.org/home-page/genetics-info/coat-color/cryptic-merles

https://www.ashgi.org/understanding-merle-and-the-science-behind-it


These are all from the Australian Shepherd Health Institute.

 

[NatJ]

What I want to know is why. How does the gene cause all these problems? Is there a good book that would address this?

Several sources say that merle in dogs is similar to Waardenburg syndrome in humans (not identical, but similar enough that it keeps getting mentioned.

I looked at the wikipedia article on that:
https://en.wikipedia.org/wiki/Waardenburg_syndrome

And I found these bits:

Waardenburg syndrome is caused by mutations in any of several genes that affect the operation of neural crest cells in embryonic development.

The neural crest is a group of temporary migratory cells that are left over after the neural tube has closed (neurulation), around the fourth week of embryonic development. They are responsible for differentiating into a diverse group of cells that reach different areas of the body. The neural tube and neural crest are derived from the ectoderm; the neural tube goes on to form the brain and spinal cord, while the neural crest cells eventually go on to form various bones and cartilage of the skull and face by migrating through the pharyngeal arches. They also differentiate into the stria vascularis of the cochlea, the nerves and glia of the intestines (myenteric plexus), Schwann cells, which myelinate the peripheral nervous system to allow sufficient conductivity, odontoblasts, which produce dentin deep in the teeth, some neuroendocrine cells, connective tissue around the salivary, lacrimal, pituitary, thymus and thyroid glands, connective tissue of the eye, such as the stroma of the iris and cornea and the trabecular meshwork, and melanocytes, including those in the stroma of the iris that give rise to brown eye colour through melanin. Neural crest cells also have a role in muscle formation, including the wall muscle of certain cardiac arteries.

What I think that means: Waardenburg syndrome in humans changes a group of cells at a very early stage of development. Those cells go on to do many different things, not just make colored pigment, so changing them can cause many kinds of problems.

So IF Merle in dogs has the same mechanism, that would be how it affects eyes and ears and other things as well as color: by messing with cells at a very early stage, before they go on to form parts of many different organs and structures.