Many people hope that their puppy will be happy, healthy, and well-adjusted. We invest in training, get all the vaccinations and toys, and even do some research.

What we don't always realize is that a hidden health risk can be written all over our pup, and we might not even notice!

While not always the case, there are certain risks associated with the coat color called "merle," especially when the pup comes from a disreputable breeder (which means that he is breeding only for money and without regard to the health of his animals).

Too many people are confused about the specifics of this problem, sometimes assuming that dogs with a lot of white and blue eyes are deaf, or sometimes not understanding that there is any risk involved at all with the breeding of these dogs.

Merle is a gorgeous coloring pattern found in the breed standard of many breeds of dogs. Among some of these breeds are: Australian Shepherd, various Collies, Catahoula Leopard Dog, Welsh Corgi, and the Shetland Sheepdog. It's also sometimes called "dapple," mostly in Dachshunds.

A merle dog usually has a single-colored base coat with different-colored speckles, spots, or patches. The merle gene can also cause a dog to have blue or multi-colored eyes and/or foot pads with patches of pink and black.

In order for a pup to come out merle, at least one of his parents must carry the merle gene. One merle parent, though, does not necessarily guarantee any merle puppies. As with most genetics, it is often luck of the draw.

Because of this, the merle pattern is often considered more "rare" than other possible colorings in any one breed. And rare -- because of supply and demand -- usually means "worth more money" to breeders, both responsible and otherwise.

Why not just breed two merle dogs together, then? This would ensure that there would be at least some merle puppies, right, and therefore the breeders would make more money (or charge less)?

While, yes, breeding two merle dogs often results in many merle puppies, the results are almost never desirable. This is because, statistically, a quarter of the produced puppies will be "double merle" or "lethal white" (another quarter will be non-merle, and the last half will be single merle).

The problem with these double merle (or double dapple) dogs is not in their gorgeous coats, but it is in the genetics that cause them. See, the genes that determine a dog's coloring also have a huge role in the development of his hearing and eyesight.

Lethal White in a dog is not actually deadly, unless you count the pups that breeders "cull" (euthanize after birth because of an unwanted trait). It also rarely results in an entirely white dog; usually a double merle pup will have at least patches of merle somewhere on its body. The title, therefore, is really a misnomer. The dogs are usually neither white nor doomed to an untimely death because of their genetics.

But misnomer or not, it can cause serious problems for the pups in its category, namely deafness or blindness, and even both! Pups born "lethal white" can also have malformed eyes or no eyes at all.

Disclaimer: "Lethal White" in dogs is very different from Overo Lethal White Syndrome in horses; the causes and effects of the two are completely unrelated to one another.

Thousands of American families have dogs that are deaf, blind, partially one of the two, or any combination thereof. Handicapped dogs make great pets once you learn how to accomodate them.

This means that adopting a puppy deemed "lethally white" is not a bad idea; you just need to understand the risks and be prepared to deal with them. Double merle (or "double dapple") pups often have gorgeous color patterns, too.

So there's nothing wrong with a deaf or blind dog... as a pet.

But no breed club or registry will accept a genetically deaf or blind dog in its conformation ring. After all, a dog that has a genetic defect is not showing the standard of the breed.

This means that no reputable breeder would ever allow two merle dogs to mate and produce puppies, even if they try to convince you that it is "safe". The risks are too great to them. A huge red flag should shoot up if you encounter, say, an Australian Shepherd "breeder" with all merle pups and adults. Do your research, and never support the creation of sick animals with backyard breeding and puppy mills.

The only way to eradicate merle-to-merle breeding is to never endorse disreputable breeders who are only "in it" for the cash they can make off of these "rare" dogs.

Remember, this genetic problem is completely avoidable through responsible breeding practices. And while a dog with a genetic defect does not necessarily make a worse pet, it should never be intentionally bred now that we know about these dangers.