How does paternity testing work?
You get half your genetic information from your mother and half from your father. To carry out a paternity test, scientists take a pinprick of blood from the child, the mother and the supposed father. Half the DNA fragments that make up a child's STR profiles come from the mother and half from the natural father. If the child's STR profile contains fragments that can't be matched to the supposed father, he can be ruled out as the child's natural father.