Dictionary: January 2009 Archives

The paternity test results will show the allele (see DNA Dictionary for explanation of allele) size for the parties who participated in the test.  When mother, alleged father and child are included in the DNA paternity test, the alleles that the child received from the biological father (called the obligate paternal alleles) can be determined by subtracting the mother's contribution to the child's DNA.  If the alleged father does not have the obligate paternal alleles at three or more loci, he is excluded as the biological father of the child.  If only a child and alleged father are tested, and they do not share any common alleles at three or more loci, the alleged father is also excluded.  When the alleged father contains the obligate paternal alleles at the loci tested, then he is not excluded as the biological father of the child. 

There are cases, where test results show a non-match for one or two loci.  This may indicate mutations which will require additional analysis but it may also indicate that a close biological relative of the tested alleged father (such as a brother, father or son) may actually be the biological father of the child.  Additional calculations can be performed to help address this possibility.  However, it is best to have all possible alleged fathers tested to establish the true biological father.  DNA testing facilities can offer you Paternity Testing with additional samples prices so that anyone thought to be the alleged father can be tested.  Talk to your local DNA expert about the circumstances of your case, so that discretion is used during the actual collection.

The final results will indicate the Probability of Paternity expressed as a percentage.  This percentage is called Paternity Index (PI).  The PI is calculated  using a "prior probability of paternity" of 0.5 in the calculation  This prior probability is a neutral value (without bias) that assumes the alleged father is as equally likely to be as he is not to be the child's biological father.  A DNA test results iwth 0% PI means that the alleged father is excluded, or cannot be the biological father.  A PI of 99% and above means that the alleged father is most likely the biological father.