How DNA Paternity Testing Works

DNA testing science is used today to help determine who the father of a particular child may be. While there’s no way to determine with 100% certainty if there is a genetic link between prospective father and child, modern DNA tests are accurate enough to make determinations with 99.9% certainty.

Paternity testing takes into account the way DNA is constructed. Except in the case of identical twins, everyone walking this planet has a unique DNA fingerprint. The base code of DNA is written with four letters – A, C, G, and T – which stands for the molecular compounds known as Adenine, Cytosine, Guanine and Thymine. These four compounds combine in a unique way in nearly everyone, but since 50% of your DNA comes from your father and 50% of it comes from your mother, you can compare your DNA to your parents and expect a high degree of overlap – much more than you would expect from a stranger.

DNA paternity testing involves taking a sample from the prospective father, a sample from the child, and often a sample of the mother. Once all three samples are processed, the DNA chains – the ways that those four letters combine over and over – are compared. High levels of similarity between the ways a possible father’s DNA combines and the ways a child’s DNA combines is enough to determine paternity, especially when the DNA of the mother is taken into account.

Of course, just taking DNA samples isn’t always enough – at least when it comes to legal determinations of paternity. While science doesn’t lie, people do, and often; someone looking to avoid having to be legally responsible for a child he fathered could easily have his DNA sample tampered with or replaced with someone else’s unless there are rigorous controls set in place. This is why, in legal matters, a neutral third party has to be involved in collecting the DNA samples to preserve what’s called the chain of custody. This chain needs to remain unbroken to prove no one could have gotten their hands on the DNA samples that weren’t authorized to do so before the results are sent to the courts. It is then – and only then – that the scientific certainty of the results of a DNA paternity test can be matched with its legal certainty.



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