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So when a new breeds of dog are bred, this is all the result of mutations, not changes in gene expression? How is it that domesticated dogs of nearly all breeds will revert back to a single form in a relatively short period of time when released into the wild?

"So when a new breeds of dog are bred, this is all the result of mutations, not changes in gene expression? How is it that domesticated dogs of nearly all breeds will revert back to a single form in a relatively short period of time when released into the wild?"

They don't all revert back to a single form. In the process of selective breeding, there were mutations that made some of the dogs more like what the breeder wanted. New alleles can and do form. Speaking from experience, there are known mutations in tropical angelfish that have led to new color and fin patterns. With a homozygous pair, they will breed true. Their descendants will not revert to *wild type* as those wild type alleles are not present any more in that pair. And I never said that all change in genotype or phenotype is a result of mutations. I just stated the fact that mutations, which are mostly neutral, can add information that wasn't there before.

How is it that domesticated dogs of nearly all breeds will revert back to a single form in a relatively short period of time when released into the wild?

One of the first things that will happen to a truckload of domestic dogs released into the wild is that most of them will die, particularly the miniatures and toys. The ones closest to wild dogs will be the most likely to survive and breed.

There is nothing inconsistent with domestic animals being the result of both selective breeding and mutation.