DNA paternity test results are determined by taking samples of DNA from the father and comparing them to the DNA of the child, explains Genetic Profiles Corporation. If the genes in the child's DNA are also present in the father's DNA, then the father and the child are biologically related.
First, the child's DNA is compared to the mother's DNA, as Genetic Profiles Corporation explains. Genes that are present in the child but not present in the mother must, therefore, belong to the father. These genes are compared to the father in question, and matching genes prove that he is the biological father, while a lack of matches proves that he is not.