Sheltie color question

GeeRome said:
Now, in my opinion, a responsible breeder would not take the risk of producing a blind/deaf pup for the sole purpose of color. So if breeders are making that choice, I would not list them as reputable and responsible. As getting one pup of a really pretty color should not take presidence over the health of the whole litter. You are condemning pups to a life-altering disability just at the chance of getting a pretty color. Not a responsible decision in my opinion. Sure, the breeder gets a nice color for their dog, but who winds up caring for the disabled dog for the rest of their lives? Or does that disabled dog jsut get hit over the head and forgotten about?
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GeeRome I would be the person who gets to take care of them. I had a lady offer me a what she called "double dilute" once. The dog was blind, deaf and had many medical issues. At the time she asked me to take her, I was just starting my rescue and was not knowledgeable enough to take her.
 
I agree! I would never breed two merles togather just because I wouldnt want to take the risk on health problems with the pups. its funny though the breeder I got belle from is ok with merle-merle breedings if done carefully but mention a merle-sable breeding and its the end of the world :rolleyes2: I would rather see a merle-sable breeding done than merle-merle breeding!
 
I have to ask....why is breeding two merles an issue but not breeding two sables or two tri's?

I'm just curious....I would love my next pup to be a merle, so I want to know what to watch out for.
 
BarbV said:
I have to ask....why is breeding two merles an issue but not breeding two sables or two tri's?

I'm just curious....I would love my next pup to be a merle, so I want to know what to watch out for.
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Hey Barb,

It's all about the inheritance of the genes involved. Merle is controlled by the PMEL17 gene (also called SILV) and follows a codominant pattern of inheritance. That means that if the dog has two copies of the "normal" gene (m/m), it is not merle. If it has one copy of the normal gene and one copy of the mutant gene (M/m), it is merle. If it has two copies of the mutant gene, (M/M) then it is "double merle". Double merle dogs appear predominantly white with small regions of merle, and also tend to have vision and hearing problems, among other potential developmental and structural defects.

The gene that controls the "base" colors in Shelties (sable, tri, bi-black) is controlled by the ASIP gene and follows a normal dominance hierarchy, with sable dominant to tri, and tri dominant to bi-black. The ASIP gene does not have the same developmental issues associated with it that PMEL17 does.

So when looking at Mendelian genetic inheritance in the case of merle:

If you breed two non-merle dogs (so that would be sable, tri, or bi-black) you would only get non-merle pups.
m/m X m/m = 100% m/m, each parent can only give the m allele so all pups are m/m

If you breed a merle dog (blue merle, sable merle, bi-blue) to a non-merle dog (sable, tri, bi) you will get approximately 50% merle dogs and 50% non-merle dogs.
M/m X m/m = 50% M/m and 50% m/m

If you breed a merle dog (blue merle, sable merle, bi-blue) to another merle dog (blue merle, sable merle, bi-blue) you will get approximately 25% non-merle dogs, 50% merle dogs, and 25% double merle dogs.
M/m X M/m = 25% m/m, 50% M/m, 25% M/M

The same genetic principles hold true for the ASIP alleles, but the difference between ASIP and PMEL17 is that there are no structural or vision/hearing problems associated with ASIP. It's purely coat color.

Hope that makes a bit of sense.
 
Thanks for the clarification (I think?!)

I'm going to need to map this out on a piece of paper, but I think I get it.

I guess its not really on issue for me, since I do not ever plan on breeding - I am just thinking about getting a merle. But at least with this info, I can check out the pedigree for other potential deficiencies that might come into play later in life.

I'm not a biologist by any stretch so I'm going to play this back to you in layman's terms:

- A merle gene is something like a mutant gene? And breeding merle to merle can replicate dormant "strong" genes that could lead to blindness, deafness?

I'm trying to dummy it down because I'm so tired of b/y breeders wanting to breed their pups (on yahoo, dogster) with no clue as to what they are doing.
 
BarbV said:
- A merle gene is something like a mutant gene? And breeding merle to merle can replicate dormant "strong" genes that could lead to blindness, deafness?
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Hmm, not quite.

Each trait that a dog has is controlled by a particular gene or group of genes. So when looking at coat color, there are a number of genes that all interact with each other to produce the different colors that we see in Shelties.

The main colors that Shelties have (sable, tri, bi-black) are controlled by a gene called ASIP. There are different mutations within that gene that differentiate between sable, tri, and bi-black.

Merle is controlled by a different gene and can sort of go "on top of" the other base colors for Shelties. The gene that determines whether a dog is merle or not is called PMEL17. If the gene is normal with no mutations, then the dog is not merle. If one copy of the PMEL17 gene has a mutation but the other copy is normal, then the dog is merle. If both copies of the PMEL17 gene have a mutation, then the dog is "double merle".

There is no real link between ASIP and PMEL17, only that they can be applied in layers. For instance looking at a blue merle, the dog is a tri-color dog, so that is the first layer. Then the merle is like a second layer on top of the tri-color. Making the final result blue merle.

The reason that the merle mutation can cause other developmental issues is that PMEL17 not only impacts coat color, but also nerve cell migration and development. So where a mutant in ASIP will only result in the dog being a different color, a mutation in PMEL17 changes the dog's coat color in addition to changing their development, resulting in eye/ear issues as well.
 
That's sorta, kinda, maybe what I meant! :smile2: In my simplistic terms!

Thanks for this. We all learn from these kinds of postings.
 
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