Most veterinary practitioners are faced with questions from owners regarding the genetics of their pets on a daily basis.
Discussions include the risk of disease in certain breeds, assuredness of genetic heritage, and the breed assignment of mixed-breed
pets with unknown parentage. Thanks to the advent of genetic DNA typing, practitioners are increasingly empowered with the
means to answer these questions. Perhaps of most interest to practitioners is the ability to more accurately determine genetic
disease risk. As in human medicine, the potential exists for personalized medicine for veterinary patients in which medical
care is tailored to the individual patient based on his or her genetics. Practitioners interested in providing comprehensive
care to their patients can now offer genetic testing as well as be a knowledgeable reference on the subject to their clients.
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Genetic tests are available for many different domesticated species; however, in this article, I primarily focus on dogs.
These tests include breed identification, parentage testing, phenotypic trait testing such as coat color, and genetic disease
testing. This article focuses on those tests most relevant to practitioners, such as canine genetic disease testing, and includes
information on the basic hereditary of genetic traits as well as an explanation of the science behind these tests.
CANINE GENOME
Studies into the origins of domestic dogs show a direct descent from wolves at least 14,000 years ago in probably two separate
domestication events.1 Most modern dogs appear to have originated from the Middle Eastern wolf, with the basenji claiming the title of the most
ancient breed in existence today.2,3 With the founding of The Kennel Club of Great Britain in 1873 and the American Kennel Club in 1884, breed registries were
established. Soon to follow was the advent of the breed barrier rule in which both the sire and dam had to be recognized members
of a breed for offspring to be eligible for registry. Thus, breeds arose from a limited genetic pool of animals that continue
to be genetically isolated from each other.3
The selective breeding of this limited genetic pool has led to a spectacular diversity of phenotypic traits in dogs, part
of what makes them such interesting partners to people. However, it comes with a downside—a high incidence of genetic diseases.
Researchers have been investigating the genetic causes of heritable diseases in dogs since the 1960s.4 Technological advances and enhanced DNA database availability have increased the efficiency and ease of this research. The
first canine genome was sequenced in 2003 by using DNA from a standard poodle.5 Since then, more in-depth sequencing has been performed and greatly expanded to include DNA from other breeds. Access to
the genome sequences of multiple breeds has the potential to transform veterinary medicine by providing unique populations
in which to study genetic diseases, ultimately leading to a better understanding of these diseases. Through genetic studies,
the genes of breeds predisposed to certain diseases can be compared with the genes of resistant breeds. This limits the effects
of enormous genetic diversity unrelated to the disease of interest that exists in the human population. The power of this
type of analysis has made the dog a particularly attractive means to research diseases common to both dogs and people for
the benefit of both.
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