Forensic genetics and the UK's national DNA database
29 November 2005
Dr. Peter Gill, Forensic Science Service, UK
Currently STRs are the workhorse national DNA databases (NDNADs) worldwide. In the UK more than 3 million samples have been DNA profiled. Other loci are in common use and these include mitochondrial DNA, Y chromosome markers and autosomal single nucleotide polymorphisms (SNPS). Recently, there has been much debate about the efficacy of STRs in relation to alternative methods. Bearing in mind that there may be limited sample available, multiple tests are often not possible, hence a decision making process is needed about which to use. Recent European collaborative exercises have demonstrated that improved results can be obtained from smaller amplicons and this has led to much interest in the development of 'mini-STRs' where amplicon sizes are much reduced.
New extraction methods (laser micro-dissection) enable single cells to be physically picked from microscope slides. The low copy number technique, which simply uses elevated number of PCR cycles, is sensitive enough to analyse single DNA copies, but difficult interpretation issues (such as contamination) are raised with very sensitive methods. We have increased our understanding of LCN systems by developing computer simulations of the PCR process.
To facilitate interpretation of conventional DNA profiles, mixtures and LCN profiles we have developed new expert systems. In addition, a novel approach known as 'familial searching' has also been used. This method has been successfully used to identify relatives of perpetrators not on the NDNAD and has led to successful convictions.