The primary goal of parentage testing is to identify the biological parent of a given child. It is done to determine an individual's parent or parents in, for example, cases of adoption or alleged paternity. This determination must be looked at very carefully and must identify the alleged parent with at least 99% certainty.
Many different types of laboratory tests can be done to assess parentage, including examination of red blood cell antigens (blood typing), examination of polymorphic serum protein genes, and assessment of short tandem repeats (see previous page). The DNA testing techniques used are similar to those used in identity testing for a criminal investigation, that is, extracting DNA from cells and manipulating it in such a way as to be able to examine the individual uniqueness of it.
If, after testing multiple systems, the parent in dispute is not excluded as a possible parent, a mathematical estimate of the possibility that the tested person could be the biological parent must be calculated. This mathematical testing combines the results of the genetic tests with other "non-genetic events" (location of the alleged parent at the time of conception, phenotype of the parent and child, etc.) and results in a "parentage index." This index is a percentage of the likelihood of parentage. Results of these tests are admissible as evidence in court.