5.5.3.6 PCR-Based Methods. The discovery of short tandem repeats(STRs) together with the
introduction of automated sequencing technology has led to the current powerful systems for the identifi-
cation of individuals. Human forensic casework is now carried out using commercially developed auto-
somal STR multiplexes(single-tube PCR (Section 5.2.2) that amplify multiple loci) and is established
worldwide because of its advantages of high discriminating power, sensitivity, ability to resolve simple
mixtures, speed and automation. The resulting reduced cost has paved the way for the creation of national STR
DNA databases (http://www.cstl.nist.gov/div831/strbase/). For example, the UK National DNA Database
contained some 2.5 million reference profiles and about 200,000 crime-scene profiles as at July 2004
(http://www.forensic.gov.uk/forensic/news/press_releases/2003/NDNAD_Annual_Report_02-03.pdf).
Automated sequencing equipment for multiplex analysis typically uses multi-channel capillary elec-
trophoresis systems that detect fluorescently labelled PCR products. These are combined with robotics
Nucleic Acids in Biotechnology 183
Figure 5.11 The evolution of DNA typing systems. (a) The very first DNA fingerprints with a family group at left (M,
mother; F, father; C, child) plus DNA from various non-human species. (b) Improved DNA fingerprints
from a single family with the father (analysed twice) and his 11 children. Note how DNA fingerprints read-
ily distinguish even close relatives and how bands in the missing mother can be easily identified as bands
in the children that are not present in the father. (c) Simpler DNA profiles of unrelated people. (d) DNA
profiling using PCR-amplified microsatellites. Several microsatellites are amplified at the same time and
the resulting profiles are displayed on a computer and automatically interpreted for databasing
(Courtesy of Orchid-Cellmark^13 ; A.J. Jeffreys,Genetic Fingerprinting, The Darwin Lectures 2003,
Darwin College, University of Cambridge, 2003, 49–67. © (2003), with permission from Cambridge
University Press)