What defines a "direct exclusion" in relationship testing?

A "direct exclusion" in relationship testing occurs when a genetic marker, which is present in the child, is completely absent in both the mother and the alleged father. This finding strongly indicates that the alleged father cannot be the biological father of the child since the child possesses a trait that neither parent has. In the context of paternity testing, both parents must contribute genetic information to their offspring, so if the child has a specific genetic marker that is not present in either parent, this effectively excludes the alleged father from consideration as the biological parent.

This scenario is critical in genetic testing, as it provides definitive evidence in cases of disputed paternity and helps to clarify parental relationships based on genetic contributions. In contrast, other combinations of genetic markers do not yield such clear exclusions and may allow for the possibility of paternity under certain circumstances, as they could suggest shared genetic ancestry.