How DNA Testing Works

DNA Testing: a Powerful Tool for Identification

DNA is the genetic “blueprint” that makes us who we are. Only identical twins share this blueprint; everyone else is genetically unique.

DNA testing works by looking for DNA matches between two biological samples to prove a relationship between individuals. These biological samples are collected from the cells on the inside of your mouth using a cotton swab.

The test analyses certain parts of the DNA molecule, known as STRs (Short Tandem Repeat), which are chosen for their variability between different people. We generally analyse between 16 and 24 of these STR DNA markers.

Since everyone inherits half of their DNA from their mother and half from their father, related individuals are more likely to share the same version of these genetic markers than people who are unrelated. The probability of two people being related can be calculated using the frequency of their DNA pattern in the general population.

For example in the case of paternity testing, since a child has inherited one half of his or her DNA from the mother and one half from his or her father, if the man tested shares one gene copy with the child at each DNA marker then there is a greater than 99.99% chance that he is the biological father.

If he does not share a gene copy at two or more DNA markers then he is not the biological father of the child.

In rare cases, a biological father may not share a gene copy with his child at one DNA marker as a result of a mutation which we can account for our analysis.