The paternity test is based on the analysis of human genetic material, deoxyribonucleic acid (DNA). DNA is a linear molecule in which we examine sections called STR-type markers. These have different lengths in different individuals. The length of the stretch is referred to as an allele and is expressed as a number (e.g., 5, 8, 23, etc.). Each individual has two alleles of a given system, and the child always inherits one allele from the mother and one from the father. Thus, in each system, the child must have one allele identical to that of its biological father. In this test, we examine 16 STR markers, plus one additional section to determine the sex of the sample.
Paternity of a marked male is excluded (in a given system) if the marked male does not have either of the pair of alleles that the tested child has in that system. Due to the rare possibility of a random heritable DNA change - a mutation - paternity is only considered reliably ruled out when at least two STR systems rule it out. If paternity is not excluded in this way, the paternity index (PI) and the probability of paternity (W) are calculated (from known data on the frequency of each allele in the population). With a sufficient number of STR systems examined, the probability of paternity borders on certainty - at least 99.99% (“paternity virtually proven”). The same principle applies to the DNA maternity test.