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.