DNA Testing Explained

DNA Testing can take lots of forms. It is based on the use of DNA molecules, which exist within the cells of all living things.

DNA stands for deoxyribonucleic acid and it contains a code that tells the human body everything it needs to do to grow, live and adapt.

A persons DNA molecule is unique to them, just like a fingerprint. So, while humans share lots of physical traits, this is why we are still different to each other in many ways. It is because of this that DNA testing is so useful. It can be used to identify a person, to place a person at a crime scene and DNA testing can also be used to identify biological relationships.

For all of these DNA testing applications, a DNA sample is collected, analysed and turned into a DNA profile.

Sample Collection for DNA Testing: For applications such as paternity testing, the DNA test sample is usually collected using a mouth swab. Our cheek cells, like all our skin cells, each contain a full copy of our individual DNA molecule. The mouth swab is quick and painless, so it is the preferred method used by all testing laboratories.

DNA test samples can also be found in many other samples. These would generally be termed as Forensic DNA testing samples

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Creating a DNA Profile: When DNA has been extracted from a sample, the DNA is tested to create a DNA profile of the donor. To do this, scientists look at small portions of the DNA called Alleles. When a scientist looks at a piece of DNA, they can analyse the alleles they find. The alleles are identified and given a unique number. These numbers represent a person’s DNA profile.

At each location on the DNA molecule, a person has two alleles. Therefore when looking at a person’s DNA profile, you will see two numbers for each location on the DNA molecule analysed.

Why can DNA testing be used for Paternity Testing:

    A persons DNA is usually stored as a complete molecule in the body, with a few exceptions. One of these exceptions is the DNA found in the Egg of a woman and Sperm of a man. The egg and sperm only contain half of the DNA molecule. At the point of conception, a child's DNA is formed. This is done by the DNA in the egg and in the sperm coming together to form a new DNA molecule that is unique to the child that has been conceived. Half of the DNA comes from the mother (from the egg) and half comes from the father (from the sperm).

Therefore, when we look at a child's DNA profile, one of the numbers (as mentioned above) at each of the locations tested, will match one of the numbers at the same location for each biological parent. (i.e. Half the alleles (numbers) will match exactly to the DNA of the biological mother and the other half will match exactly to the biological father.)

Why can DNA testing be used for Maternity Testing:

    The same rules apply to maternity testing as they do for using DNA testing for the purpose of paternity testing. Please see above.

Using DNA testing for testing other Biological Relationships:

    DNA testing can be used to look at lots of biological relationships that are further removed from an individual than a Paternity test, which looks for a direct biological parent.
    DNA tests for Siblings can determine between individuals who have the same father and mother, and who only have one biological parent in common. DNA testing can be performed to establish if someone is the Aunt of a child or the Uncle of a child and of course DNA can also be used to find whether someone is the biological grandparent of a child.
    DNA testing has become so advanced that conclusive answers can now be found to provide evidence of biological relationships spanning all the way to 4th cousins.

Tests such as DNA tests for Siblings, Grandparents, Aunts and Uncles are all much more complex DNA tests than the Paternity tests. Unlike in a Paternity test or Maternity test, participants are not expected to match at all locations on the DNA molecule. This exact match only occurs in direct parentage relationships as explained for the Paternity test above.

The DNA relationship tests such as Sibling tests are based on the fact that biologically related individuals will have more DNA in common than those that are unrelated. The amount of common DNA depends on how closely the individuals are related. The DNA test will and this is how the DNA test can determine between one sort of relationship to another.