With all the information on various laboratory blog sites, I thought I would go back to a basic and review how to read the paternity test results.
The paternity test results will show allele (see DNA Dictionary for explanation of allele) sizes for the parties who participated in the test. If the test indicates no allele size, it is considered that the same allele size is present at both loci. 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. While it is not necessary to have the mother tested to confirm Paternity, it is obviously a better choice to have all 3 parties tested so at least the mother's DNA is a known factor in the paternity index and probability of paternity figures.
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. Always, let your DNA collector know the circumstances of your case and if there are possible related males involved in the paternity. Additional calculations can be performed to help address these factors. 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 with 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.
When using a local DNA collector, you have the ability to ask questions before, during and after the DNA collection process. Take the time to understand what the results indicate - in the long run - when you doubts are erased - the child involved in the test will be given a solid foundation on which to build their life.