Basic issues in forensic DNA typing.

DNA analysis has become the standard method in forensic stain typing (termed DNA profiling). In contrast to conventional serological methods, any human tissue or body fluid can be analysed by DNA profiling as long as it contains nucleated cells. The majority of genetic systems studied at the DNA level are derived from "non-coding" portions from the human genome, and are located either in the vicinity of expressed (coding) genes or in stretches of DNA sequences interspersing with the genes. The typing results are usually recorded as DNA fragment lengths or "alleles" indicating the number of core repeat elements for short tandem repeat systems. These typing results do not contain any useful information which might reveal genetic traits or predispositions for inherited disease about the individual studied. Typing systems for DNA profiling are predominantly selected according to criteria related to the robustness for typing of (potentially degraded) forensic specimens, the degree of genetic polymorphism (which influences the chance to exclude a wrongfully accused person), and the amenability to standardisation as a basis to obtain reproducible results.