A Linkage Test is a genetic analysis method used when the specific mutation can not be tested. When we are unable to test for a causative mutation (a single mutation known to cause a health condition or trait), we look at DNA sequences around a known causative mutation to see if it matches the DNA sequences of dogs already known to have said mutation and the associated genotype. In a newly tested dog, we can generally infer if the causative mutation is present or not, based on the DNA sequences looked at in the linkage test.
There are some types of mutations that cannot currently be directly assayed using our genotyping technology. However, DNA behaves in such a way that we can test sets of markers around these mutations and use that information to infer a genotype that we cannot assay directly. Because these mutations are physically linked to one another, we can use models to indirectly test for those mutations that we cannot directly assay.
One fun way to imagine the process is to picture a dog. If you see a Golden Retriever's head and tail, you can infer what the body is going to look like even though you can't see it. Because there is an element of randomness to how DNA is shuffled around during mating, there are rare cases where the dog's body won't match expectations, but almost all of the time you could predict the body type by looking at the head or tail even if you cannot see the body directly. Our linkage tests work the same way.
Embark's linkage tests have demonstrated high accuracy, typically being around 98 or 99% predictive of the true genotype. When such tests are employed for specific genetic analyses, Embark ensures full transparency by indicating the use of linkage tests in the results provided to customers. Some examples of traits that can be assessed through linkage tests include Intervertebral Disc Disease (Type I) Risk, Blue Eye Color, and Furnishings.
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