The paternity testing process works by comparing the DNA of a child and an alleged father to investigate their biological relationship. Whilst one might think that the whole strand of uncoiled DNA is analyzed for a paternity test, in reality this is not the case. In practice, only certain regions on the DNA, called microsatellite markers or loci, need to be compared to establish biological paternity. Microsatellite markers are short fragments of DNA in which the same DNA sequence is repeated several times. Since an individual has two genetic complements of DNA, there are actually two copies of each marker present, one inherited from each of the biological parents.
Nowadays given the level of improvement in the science behind the test, the analysis of 16 microsatellite markers has become standard in paternity testing. The microsatellite markers used are standard markers recommended by specialised organisations such as the European Network of Forensic Science (ENFSI) and Interpol. An important property of these markers is that the number of DNA sequence repetitions (or frequency) is highly variable within the general population but remains relatively unchanged from parent to child. As a result, the frequency of one complement of each of the child’s markers matches that of one complement of the biological mother, whereas the frequency of the other complement matches that of one complement of the biological father.
The set of frequencies of the analysed markers constitutes the genetic profile of a tested individual. A standard paternity test determines the genetic profiles of the mother, the child and the alleged father. By comparing the three profiles it is possible to identify the marker in each complementary pair that the child inherited from the biological mother. By elimination, the remaining half of the genetic profile was inherited from the biological father. By comparing this part of the child’s genetic profile with the profile of the alleged father, the Paternity Test determines whether the alleged father is the biological father or not. A match between the two profiles indicates that the alleged father is the real biological father. On the other hand, if the profile of the alleged father does not match that of the child, he is excluded from paternity.
Click on the following link to read more about the Accuracy of Paternity Tests.
