How the Testing Works

The DNA Testing Concept

The concept of DNA testing is based on the fact that:

• All cells in the body have a nucleus containing deoxyribonucleic acid (DNA).
• DNA carries the genetic information that produces the distinct characteristics of each person.
• The DNA molecule will differ from person to person, except in cases of identical twins.

Parentage Testing

It is scientifically accepted that a child inherits half its DNA pattern from the mother, and the other half from the true father.

The testing steps are:

• A portion of the child’s DNA fingerprint inherited from an undisputed parent is identified through a comparison of the DNA profilest.
• The remainder of the child’s DNA (inherited from the other parent) is compared with the DNA of the alleged parent.
• If there is no match, s/he is excluded from parentage and analysis need not proceed further.
• If there is a match, s/he is included as a potential parent of the child.
• The DNA patterns are then subjected to comparative statistical analysis that allows the probabilities of relatedness to be calculated.
• The goal of the testing is to produce at least a 99% probability of relatedness.

About Comparative Statistical Analysis

For a man not excluded from paternity, three statistical values typically appear on reports that summarize the findings. They are the:

• Parentage index
• Probability of parentage
• Prior chance of parentage

Parentage index
This refers to the genetic odds in favor of Parentage. An index of 5 indicates that the alleged parent is 5 times more likely to be the parent of the child than an untested, random individual. The combined index reflects the total odds and results from multiplying the individual paternity indices together. A combined index of 600 indicates that the alleged parent is 600 times more likely to be the true parent than an untested, random person.

Probability of parentage
This is derived from the combined parentage index and restates the alleged parent’s likelihood of relatedness as a percentage. The formula used to calculate this percentage requires that a value be assigned to one of its terms called the prior chance of parentage.

Prior chance of parentage
This is the chance the alleged parent is the parent before the genetic testing is performed. On a national average almost 70% of alleged parents end up being the true parent. In order to maintain neutrality, our laboratory uses a 50% prior chance in our interpretation of the test results. This means that we base our opinions strictly upon the DNA test results and do not typically consider non-genetic information either for or against the allegation of parentage.

The statistical results of testing described above are produced for paternity testing, maternity testing, and in essentially every other type of relatedness test performed (including sibships and distinguishing between identical and fraternal twins). Our laboratory also has the capability of establishing parental relationship by reconstruction. In such cases, testing of other family members can establish or refute parental relationships when the alleged parent is not available for testing because of death or other circumstances.

If you decide to have testing done, we will provide you with detailed descriptions of all these procedures if you so desire.