Researchers begin a genetic map by collecting samples of blood., saliva, or tissue from family members that carry a prominent disease or trait and family members that don't. The most common sample used in gene mapping, especially in personal genomic tests is saliva. Scientists then isolate DNA from the samples and closely examine it, looking for unique patterns in the DNA of the family members who do carry the disease that the DNA of those who don't carry the disease don't have. These unique molecular patterns in the DNA are referred to as polymorphisms, or markers.