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When evaluating DNA (or any other genetic test) keep in mind that each person has two sets of genetic markers, one from their father and one from their mother. In evaluating a paternity case one first looks at what the mother and child have in common. The genetic marker that is left over in the child must come from the biological father. If the alleged father has that genetic marker, he is not excluded. If he does not have the genetic marker, he is excluded in that system.

In example A, the mother has genetic markers 3 and 4. These are the genetic markers the mother inherited from her parents. Looking at the child, the mother and child share the 3 genetic marker. The 3 is what the child inherited from the mother. The 6 in the child must come from the biological father as the mother does not have this genetic marker. Note that the alleged father has the 6 genetic marker that is needed from the biological father. Therefore, the alleged father cannot be excluded from paternity as he has the 6.

Suppose another alleged father is submitted in the same case and the results in example (B) are obtained. We have already evaluated the mother and child and know that the biological father must contribute the 6 genetic marker. The results for Alleged father #2 are not consistent with paternity, as he does not have the 6 genetic marker. (Note: normally exclusions in at least two genetic systems are obtained before excluding a person.)