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How is genetic information passed from one generation to another? Where is this genetic information stored? Why do
different breeds have different mutations for the same disease? These are just a few of the questions that breeders, pet
owners and veterinarians are asking. The answers to these questions are essential for creating canine breeding programs
that will help ensure the elimination of the numerous genetic disorders seen today.
The basic building block of life is the cell. Within the boundaries of its nucleus lies a tremendous wealth of genetic
information that is responsible for regulating the body’s organs and senses as well as determining each animals unique
physical characteristics. This genetic information is "recorded" in a biological code called DNA. Tightly
coiled DNA forms structures in the nucleus called chromosomes. Specific "groups" of DNA in the chromosome are
referred to as genes. In the cell, chromosomes appear in pairs. Each gene on one chromosome in the pair has a partner
gene on the other chromosome in the pair. Therefore, every animal has a pair of genes that influences a particular
function in the body. If the two genes that make up the pair are identical, they are termed homozygous. If they are not
identical they are termed heterozygous. Homozygous animals can have two identical mutated genes ("affected")
or two identical normal genes ("normal"). For instance, suppose the letter X symbolizes a gene. Homozygous
mutated genes would appear as xx and homozygous normal genes would appear as XX. If an animal is heterozygous (Xx), it
is a carrier of the mutated form of a gene (x) and the normal form of the gene (X). This is significant because the
animal carrying the mutated copy of the gene remains unaffected but can pass the mutated gene to the next generation
through breeding. Therefore, through genetic screening, breeders can gain vital information that enables them to create
specific breeding programs geared towards the removal of mutated genes in their litters.
What are the signs and symptoms of a genetic disorder?
An animal suffering from any
given genetic disorder can display an array of symptoms ranging from benign to debilitating. Genetic disorders are
usually chronic and progressive, (i.e. once an animal shows signs that it is affected, it will likely not recover) and
often cause death at an early age. Different genetic disorders cause distinct symptoms such as hereditary bleeding or
primary immunodeficiency problems. In contrast to infectious diseases, intoxications and nutritional imbalances that
generally affect an entire litter, genetic disorders often involve only a few individuals in a litter. Furthermore, the
age of onset of clinical signs for a particular genetic defect is rather specific and independent of environmental
factors.
How would breeders benefit from genetic screening?
Contemporary DNA-based technology
has unveiled new horizons for the identification of a genetic disorder. The development of a PCR-based methodology by
HealthGene Corp. to identify mutations provides a comparatively rapid, accurate, easy and affordable screening test. The
test takes approximately 7-10 business days to conduct and can be performed at the breeders convenience with the use of
cheek swabs, which are provided free of charge in HeathGene’s sample collection kit.
As most genetic disorders are of late-onset, it is very important to have dogs diagnosed before they pass the disorder
to the next generation. Currently, there is no treatment for genetic disorders, therefore, early detection and removal
of affected dogs from breeding programs is the only way of eliminating them. Our DNA testing not only detects affected
dogs, but also carriers of a mutated gene, which again, show no symptoms of the disorder but can pass the gene on to
their offspring.
The DNA test results we provide are easy to understand. There are three possible test results: normal, carrier, or
affected. A normal test result indicates that the mutant gene is not present in the dog. A carrier test result signifies
that one copy of the mutant gene is present in the dog. This particular dog will not display symptoms but will pass the
gene to its offspring 50% of the time. An affected test result indicates that two copies of the mutated gene are present
in the dog, and therefore, the dog will eventually display clinical symptoms.
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