is DNA evidence always 100% right?

Answer 1

DNA evidence is 100% conclusive if it determines a negative. IOW, if a DNA test on a child determines that a certain man is not the father, then that test result is 100% certain.

In cases where the DNA test shows that there is a 99% chance that a man is the father of a child, there is always the possibility, for example, that the guy has an identical twin somewhere that could have fathered the child. Identical twins have the exact same DNA. Likewise, two brothers may have almost identical DNA. More exact DNA tests have to be done if the two paternal candidates are brothers.

But, yes, for all intents and purposes, when Maury says that so-and-so IS the father, it is 100% certain, barring some sort of miracle or extremely bad luck, whichever the case may be.

Whether the DNA evidence is to determine the mother/father of a child or to determine who's blood was found at a crime scene, who raped someone, etc, the same principals applie. The results are not declared to be 100% affirmative because there is a small chance that someone in the world has the same or highly similar DNA, but that is so unlikely that DNA evidence is readily accepted in court cases as conclusive.

El Chistoso

Answer 2

There are few 100% certainties in science but the odds in favour of DNA evidence being right are pretty great because no two people have the exact same DNA fingerprint.