This DNA structure serves as a genetic marker. For each test, we determine which of the pair of genetic markers came from the mother. The other marker came from the father. When a battery of tests has been performed, we have a good genetic description of the father. If the tested man does not fit this description, he would be excluded as the father.
Courts treat exclusion results as conclusive evidence of non-paternity.
If the tested man does fit the genetic description, a probability of paternity is calculated, assuming that all else is equal. No, if DNA tests are to be done. Blood is the preferred specimen, but other tissues can be used. A convenient alternative method is to use cells taken from the inside of the cheek. However, some courts may prefer blood tests, so the parties should agree to accept other specimens.