[dragonwriter]

> Since most humans inherit exactly half of their DNA from each parent, it should be pretty obvious when 50% match the mother and the rest doesn't match either parent.

Assuming the other parent is human, or even from the same tree of life, that's not going to happen, because the actual parent will share some DNA with the purported parent; you'll never get 50% match the actual mother, 0% match neither the mother nor the putative father.

[yorwba]

Ah, right, I was only thinking about locations which are already different between mother and father.