How does the sample affect the DNA test?

How does the sample affect the DNA test?


Sample collection is the first step in DNA testing and is often done by the dog owner himself. Since a sample is a starting material for performing a DNA test, it is crucial that it is taken correctly. Samples of poor-quality cause problems throughout the laboratory procedure and in some cases can even lead to an erroneous result. To avoid problems and delays in DNA testing, we will point out the key points in sampling collection process.

The amount of DNA in a collected sample (blood, swab) is directly related to the amount of biological material. Even a few drops of blood contain enough DNA to perform a DNA test. There are more problems with buccal swabs which are not collected properly. When oral mucosa is swabbed by a collection brush mucosal cells are caught on the brush. If swabbing is to gentle or the period is to short less cells and consequently less DNA are collected. When collecting samples we advise you to insert the collection brush into the mouth of the dog between the gums and the cheek, create pressure from the outside of the cheek with your hand and rub the brush with circular movements for 30 seconds. In this way, you will avoid samples with insufficient amount of biological material from which a genetic test cannot be performed.

Another important factor in a DNA sample is its quality. When we talk about the quality of DNA in a biological sample, we primarily mean its degradation. DNA is a long molecule that breaks down into shorter pieces after a biological sample is taken. Degradation process cannot be avoided. You can imagine that DNA is a long strand that is cut into shorter pieces under the influence of various factors. Degradation to a certain point does not affect a genetic test, but once the DNA is broken down into extremely short fragments, a genetic test can no longer be performed. Because DNA degrades with time, it is important that the samples for analysis are as fresh as possible. DNA degradation is accelerated by various factors such as high temperatures, UV light, etc. Proper preparation of the sample for sending to the laboratory is also very important. It is crucial that the swab is dried before sending, because in the case of a large amount of moisture that comes out of the saliva, mold and bacteria overgrow during transport, which further accelerates the breakdown of DNA. For the sample, the worst combination is a small amount of the initial sample and intensive degradation, which occurs with improperly collected and transported buccal swabs. In blood samples, these problems are less common because the amount of starting material is much larger than in swabs of the oral mucosa.

The third important factor is an infection of a sample with foreign DNA and refers primarily to buccal swabs. This problem occurs mainly with owners who have multiple dogs living together. Due to the use of shared toys, equipment, suckling puppies and other similar reasons, the DNA of other animals is often found in the mouths of dogs living together. When a buccal swab is taken in such a case, the sample is a mixture of biological material from different dogs. The amount of biological material of sampled dog is in the majority, but genetic methods are extremely sensitive and detect smaller amounts of foreign DNA. If there is a DNA of two dogs in a sample, this cannot be detected by a genetic test, and can lead to an erroneous result. In case the dog is negative for the tested mutation and the sample is infected with the DNA of the dog that is a carrier, the result of the genetic test will be wrong (carrier). The easiest way to avoid this is to send a blood sample in such cases, but you can also do this by separating the animals living together and washing their mouth with water before taking a swab.

We have described three key factors influencing the quality of a sample to perform a genetic test. You can read more detailed sample collection instructions HERE. By following the sampling instructions, you avoid complications and delays in performing a genetic test.

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