Specimens
The proper handling of specimens for direct storage or DNA extraction and characterization is one of the most important aspects of the profiling procedure. Because DNA typing is not yet a routine test, some laboratories may perform only the isolation portion of the overall analysis and leave the other methodologies to specialized centers. Profiling may never be required for many forensic specimens and only intermediate storage needed. It is essential that smaller centers have at least the facilities to isolate, characterize, and store DNA. A broad range of DNA sources exists. Fresh tissue usually includes whole blood, buccal epithelial cells, and hair follicles. Under special circumstances, in the medical setting, the genotyping of amniotic fluid cells, chorionic villus samples, and tissue culture fibroblasts may be required. Dried specimens usually include blood and semen stains, tooth pulp, and bone marrow. Animal trophy heads and pelts are also sources of dried DNA. Preserved or unpreserved human autopsy specimens, and tissues from animal gut piles and frozen meat, are other possible sources of DNA. As with any biological test, the quality of the results can be no better than the quality of the input sample. If the DNA is highly degraded or contaminated, it may be unusable; thus, every effort should be taken to collect, record, transport, store, and isolate materials using meticulous techniques. The specimen of choice is 1 ml or more of fresh whole EDTA blood. Anticoagulants other than EDTA may be acceptable; however, there are reports that heparin interferes with the activity of certain restriction enzymes. The quantity of DNA isolated from 1 ml of blood is usually sufficient for the necessary testing and a considerably smaller sample will often suffice. There are occasions, however, when the DNA yield is low and a repeat specimen is required; for this reason it is prudent to collect an additional sample if possible. Buccal epithelial cells obtained from mouth swabs, and hair follicles are two other general sources of fresh DNA; however, the DNA may require amplification by the polymerase chain reaction to provide sufficient material for analysis.