The test compares fragments of highly variable DNA, called Short Tandem Repeats (STR). Through a series of chemical reactions, DNA from each individual is extracted. Using the Polymerase Chain Reaction technique (PCR), fifteen STR markers from the different chromosomes of the individuals tested are copied. The products of PCR are separated and detected to obtain a DNA profile.
One-half of each person’s DNA information comes from their father and the other half from their mother. By comparing the DNA profiles of the child with the mother, it is possible to establish the shared STR markers between them. The child’s STR markers not found in the mother’s profile must therefore come from the biological father.
An alleged father is excluded as the biological father if STR markers found on his DNA profile are not shared with the child’s. However if the alleged father’s profile shares common STR markers with that of the child’s then he is not excluded as the true biological father. A statistical analysis is then carried out to calculate the probability of paternity.
As shown in the test results’ table, each STR marker tested is listed together with the probability of occurrence in the general population.