How reliable is an DNA test if you only have one parent and the child?

Expert Answers
clairewait eNotes educator| Certified Educator

I'm guessing that you are asking about paternity testing.  Paternity testing can be categorized by exclusion or inclusion.  If the test done says that a man is NOT the father of a certain child, it should be 100% accurate.

The question then is how reliable is a test to see who is the father.  Testing facilities provide an accuracy rating and it is highly suggested that if you want an accurate rating you go to a facility that consistently gives 99.99% accuracy.  If the one parent you have is the father, you should be able to find a place that has a 99.99% accuracy rating.

If the one parent you have is the mother, and you are trying to determine paternity, you have a couple of options to keep a relatively high accuracy percentage.  First, you could do a viability testing - which is a test on something biological from the father (blood, hair, other body tissues).  If nothing biologically connected to the father is present, you can have a grandpaternity test done.  This is where the parents of the father are tested.

Generally speaking, the accuracy of a DNA test increases with the number of loci (locations for DNA) tested.