Forensic application of the polymerase chain reaction

Abstract

The polymerase chain reaction (PCR) is a process which allows targeted short segments of DNA sequence to be selectively copied a million-fold or more; hence the term gene amplification. It was first described in 1985 [I] and has rapidly gained acceptance as a tool in molecular biology, population genetics, genome mapping, and medical diagnostics [2]. PCR offers a number of advantages for the detection of genetic markers in biological evidence, and is emerging as the cornerstone technology for the second generation of forensic DNA analysis methods. PCR brings two important benefits to the analysis of DNA markers in biological evidence. First, amplification is possible from very small amounts of DNA. This allows genetic information to be obtained from evidence samples such as single shed hairs, swabbings from bitemarks, and the like. Second, amplification is possible from degraded DNA. This allows genetic typing to be done on the many routine case samples that contain degraded DNA, and on those special samples such as decayed body remains that previously defied genetic testing. From an operational standpoint, PCR offers two additional benefits; it is relatively simple to perform and results can be obtained within a short time frame, usually within 24 hours. PCR-based genetic typing Approaches for the detection of genetic variation in PCR-generated material fall into two general categories; those based on detecting differences in sequence and those based on detecting differences in the size of the PCR products. A number of sequence-based approaches have been described; sequence specific probing, allele specific amplification, oligonucleotide ligation, restriction site cleavage, and denaturing gel electrophoresis. Of these, sequence specific probing is the most general and the most specific in defining sequence variation at a site. The DQA typing system developed by Cetus is the best studied sequence specific probe system; it is currently available in kit form. The power of sequence specific probing is further