ELSEVIER Forensic Science International 89 (1997) 185-197 kbrensic Science Interllatiill Development of guidelines to designate alleles using an STR multiplex system P. Gill*, R. Sparkes, C. Kimpton Forensic Science Service, Priory House, Gooch St. North, Birmingham, BS SQQ, UK Received IX February 1997; received in revised form 20 May 1997; accepted 29 May 1997 Abstract We have carried out extensive validation of a multiplex system of 6 STR loci and the Amelogenin sex test to investigate the following characteristics: relative peak areas of heterozygote peaks; non-specific artefacts; stutters caused by slippage of the Taq enzyme; pull-up (an electronic artefact often associated with software). The purpose of this paper is to demonstrate how interpretation guidelines can be formulated by experimentation and analysis using casework samples. Automation allows data relating to band position (in base pairs), peak area and peak height to be easily collected and manipulated in spreadsheets or computer programs. This paves the way to designing expert systems to carry out the interpretative process. 0 1997 Elsevier Science Ireland Ltd. Keywords: STR; Interpretation; Expert system; Automation 1. Introduction The increasing use of automation enhances the prospects of computer aided systems to aid the identification of alleles. To explore the potential, Gill et al. [l] outlined a method of allele identification using a multiplex system where designations are carried out subject to two simple rules. For a given locus the distance between the alleles and respective allelic ladder markers (S,, 8,) is determined. If alleles are within +O.S bp of the respective allelic ladder marker then band shift (c) of heterozygotes is calculated (6, -6,). If ICI is greater than 0.5 bp then the designation would be regarded as inconclusive in the first instance. *Correspondening author: Tel.: 0121-607-6871;fax: 0121-622-2051. 0379.0738/97/$17.00 0 1997 Elsevier Science Ireland Ltd. All rights reserved. PII SO379-0738(97)0013 I-X