16: Analysis of Body Fluids

The chapter describes the basic principles of the current methods used in forensic laboratories to carry out human identification by DNA analysis. It commences with a brief description of the nature of biological evidence, and some alternative types of information that might be gained, before a more detailed discourse about the composition of the main biological fluids, blood, semen and saliva, encountered in a forensic context. The chapter progresses with a brief consideration of the biochemical tests used to find these different types of body fluid followed by a short coverage of the pre-DNA types of test. A detailed description of the nature of DNA and the method used to amplify selected parts of DNA is given, which includes a description of the use of polymerase enzymes and DNA primers in the DNA amplification process. The section concludes with an explanation of the use of multiplexing that allows a number of different regions to be tested at the same time and from the same sample. Following these fundamentals, several slightly more advanced themes are discussed. The nature of reporting practice and the use of a likelihood ratio are outlined, and this is further developed in the sections concerning the use of expert systems and in cognitive biases. The chapter concludes with a short discussion on recent advances.