How DNA testing works can be a bit complex, especially as it relates to determining human identity. Here, we try to help explain how the whole process works.
DNA is an acronym for Deoxyribonucleic Acid. DNA is a molecule with a helical structure that sits inside most of the cells of your body. This molecule is very fascinating because it serves as a blueprint for all the cells in your body, instructing them on how to build the proteins that act as the building blocks for your body to be constructed, repaired, and carry out its functions. DNA's instructions are written in a chemical alphabet of sorts. This alphabet consists of four "letters": A, C, T and G. Each letter represents a basic chemical that is part of the DNA structure.
There's a lot of information packed within your DNA. Each DNA strand in your body, if it were stretched from end to end, would be over three feet long. We know that certain pieces of the DNA strand - certain sequences of DNA's chemical alphabet - instruct specific proteins to be built. In between these sequences of DNA that perform useful functions, are stretches of DNA whose function scientists have not yet determined. These sections are known as "junk" DNA. Interestingly, scientists have identified certain tiny sequences of DNA that just repeat themselves over and over and over inside these stretches of junk DNA. These repeating sequences are known as short tandem repeats, or STRs. Family Genetics uses STRs to uniquely identify humans and establish relationships between people.
When you send in your DNA samples, our scientists use a technology called Polymerase Chain Reaction (PCR) to create a lot of copies of the specific portions of DNA we're interested in (a DNA profile only has 15 markers, so we don't need to look at the entire DNA strand). PCR uses precise heat and a chemical cocktail to cause the DNA to replicate itself.
Once we have enough replicated DNA to work with, we run your samples on one of our ABI PRISM 3130XL Genetic Analyzers, which look at the size of the STR sequences we've isolated and replicated, and determines your DNA profile.
When it comes to determining paternity, for instance, we look at the two profiles of the people we're testing, and see if a significant number of DNA markers are identical between the two. Since a child gets half of his or her genetic material from his or her father, they should share the 15 values we look at. While rare genetic mutations can reduce the number of shared values to 13, anything below 13 would absolutely rule out the tested man as the father of the tested child.