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Inbreeding In Man's Best Friend

By Jessica Lin


Everyday, hundreds of puppies are bought to surprise daughters, wives, sons, and fathers, as the newest addition to their family. Often times, these pups are bought from breeders selling purebred dogs at a shockingly high price. While all we see is this bundle of joy, there is so much more behind their excitatory yips and wagging tails.

In recent studies done by analyzing dog pedigrees across ten dog breeds, researchers have discovered that every breed except greyhounds yielded extremely inbred dogs. In fact, for all but three breeds of the ten studied, over “90% of unique genetic variants are lost over six generations”, which dramatically decreases the genetic diversity present in the domesticated dog. So what exactly is inbreeding and why is it bad? Inbreeding refers to the mating of closely related individuals over several generations. Continuing to do this over generations and generations leads to the increased occurrence of recessive alleles in an organism. Generally, with autosomal recessive diseases, an individual needs 2 recessive alleles, one from mom and one from dad. Thus, someone who only has one recessive allele will not be affected, yet they can still pass the allele on to their offspring. When inbreeding within an affected family for an autosomal recessive disease, the the recessive alleles become much more prevalent and there is a much higher possibility that the offspring will be affected with the disease, hence why there is such a big taboo surrounding it. However, while we are warned against the effects of inbreeding within the human population, we don’t really think about the dog population with this same philosophy. In fact, we actively condone it. Research has actually found that autosomal recessive diseases account for around 70% of all genetic diseases in dogs, many of which have orthopedic and ocular effects.

One of the most inbred dog breeds today is the English bulldog. This bulldog has been so inbred that it’s teetering on the brink of extinction. Present day bulldogs have a laundry list of health problems, some of which include poor eyesight, shortness of breath, and a variety of autoimmune diseases. The inbreeding has become so severe that it is actually rare to find an English bulldog that is devoid of these symptoms.

In an attempt to quantify the severity of the extent to which dogs have been inbred, we can compare the inbreeding coefficients. An inbreeding coefficient refers to the probability of inheriting the two copies of the same allele from both sides of the ancestry line. For example, when a brother and sister mate, the inbreeding coefficient is 25%. However, research has found that for more than half of all dog breeds, the inbreeding coefficient is above 25%, some even reaching 60%. This means for those dog breeds, they have an over 25% chance of receiving recessive alleles from both parents and thus developing a genetic disease.

It’s time to stop inbreeding and introduce more genetic diversity back into our favorite animals so that future generations can love them as much as we do.


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