If two possible fathers are related as full brothers or father and son, they may share some of the DNA markers used in paternity testing. This means that if proper precautions are not taken, both men could test positive as the child’s biological father. It is very important to let us know of a situation like this so that we may properly evaluate the testing process.
In situations such as this, the mother of the child may be required to be added to the test. If that is not possible, extended DNA testing may be required. In cases such as this, extensive analysis would be required to yield conclusive results and adding the mother would yield the highest probability to obtain conclusive results.