Dog Friendly Tips: Genetic Disorders and Defects in Dogs
Genetic defects can be a scary proposition for a pet owner, a problem that can arise through no fault of the owner's but can cause serious health problems for their pets under the wrong circumstances.
Genetic defects are recessive genes passed on to a dog down their breeding line from their parents. As a recessive gene your dog could be a carrier for the gene but never display any symptoms of a disorder but their pups might, so it is important to know the medical history of your dog and their parents before adopting a dog or breeding them. The health of a potential mate is also very important, so be sure to ask their owner about any conditions or health problems their pet or their pet's parents might have had to minimize the risk of a genetic defect rearing its ugly head. This does not mean that a condition which can be hereditary always is the result of a hereditary defect though, it could also be caused by environmental conditions, diet, or even toxins that could have been ingested by the mother during pregnancy. In addition, it's unknown why certain breeds are predisposed towards certain defects over others which is why you'll see mention of breeds that have a breed predisposition towards certain ailments.
If you suspect that an illness your pet is suffering from is the result of a genetic defect, then contact your vet about getting a family history on your pet which could reveal if the problem is genetic or if it might be the result of a disease or toxin in their environment.
Defects are passed along in four different ways, autosomal dominant, autosomal recessive, sex-linked, and polygenic inherited. Of those four, the first two are very similar. During conception and development of of a fetus, various chromosomes combine together to partly determine the animals physical and genetic make-up; defects are the result of damaged or otherwise unusual chromosomes pairing with healthy ones. Just having the aberrant chromosome makes your pet a carrier for it, even if the defect isn't actively affecting your pet's health.
When a defect is autosomal dominant, it means that your pet only needs a single copy of the gene in their DNA to suffer the symptoms related to the trait in question though, in many cases, the trait shows signs of incomplete dominance. This means that even though the trait has been passed on, it does not affect all of the pups equally and some may not even express it at all. Autosomal dominant defects are uncommon since they can be detected early, depending on the trait, and the affected dog kept from breeding and passing on the defect to further generations. Autosomal recessive is when the defective trait is recessive, meaning a pup needs to receive it from both parents before it will be expressed by the pup.
In some ways, this is more difficult to deal with since a dog can pass on the gene for several generations before two recessive chromosomes match up and the defect comes to the fore. Sex-linked defects are traits that are related to the X and Y chromosome in a pup, usually it is seen in the X chromosome since all dogs have at least one X chromosome and if this chromosome is the carrier of a defective trait then it will show up during a male dog's life time since it's the only X chromosome they have. It is less common for such defects to be expressed in females since they have two X chromosomes and, like traits that are passed on as autosomal recessive traits, both would need to bear the defect before it will show.
Of the four ways that a genetic defect can be passed on, polygenic is the least understood because of the variety of ways that it can be affected. Polygenic inherited traits are not determined just by genetics but by exercise, diet, rate of growth, and height/weight. These traits are difficult to control because how inheritable the traits are changes from breed to breed which makes it difficult to tell when a trait may be passed on and oftentimes it can go completely unnoticed or be written off as an illness and not a defect.
In any case, if your pet suffers from a genetic defect then it's important that you notify your vet and, if you adopted your canine friend, the breeder that you got your dog from in the first place. This helps vets and breeders keep track of various breeds and lineages, as well as which dogs should not breed so these defects are not passed on. Once you have and the defective trait is known, you can begin treatment for your pet and have helped future pet owners from having to deal with the same problems that you and your pet have to.
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