How DNA Matching works for finding your biological family
DNA can help adoptees and birth family members reunite by matching DNA. Since everyone inherits DNA from their parents, sequences of DNA may be shared beteween relatives. Often the more DNA that is shared, the closer the relative is to you.
Specific DNA markers, at certain locations in human DNA, contain predictable inheritance patterns which identify individuals and have been found useful in determining biological relationships. Since the markers are inherited from each parent, each person's DNA markers could differ in length and sequence from each other but more closely resemble the DNA markers of the birth parents.
Usage of specific markers helps reduce the "false positive" since 2 people can share large quantities of DNA that defines human traits or specific ethnic characterstics.