GENOTYPING OF FORENSIC SHORT TANDEM REPEAT (STR) SYSTEMS BASED ON SIZING PRECISION IN A CAPILLARY ELECTROPHORESIS INSTRUMENT

Automated fluorescence analysis of polymerase chain reaction (PCR)-amp lified short tandem repeat (STR) systems by capillary electrophoresis (CE) is becoming an established tool both in forensic casework and in the implementation of both state and national convicted offender DNA d atabases. A new capillary electrophoresis instrument, the ABI Prism 31 0 Genetic Analyzer, along with the Performance Optimized Polymer 4 (PO P-4) provides an automated and precise method for simultaneously analy zing ten fluorescently labeled STR loci from a single PCR amplificatio n kit, which provides a power of discrimination of approximately one i n five billion from a single PCR amplification. Data are presented on sizing precision, sizing accuracy, and resolution for the STR loci in the AmpF/STR Profiler(TM) kit. Sizing accuracy is highly dependent on the electrophoresis system, and therefore the reporting of alleles bas ed on the nucleotide size obtained from an electrophoresis system is n ot recommended for forensic work. The precision of the 310 capillary e lectrophoresis system, coupled with software developed for automated g enotyping of alleles based on the use of an allelic ladder, allows for accurate genotyping of STR loci. Sizing precision of less than or equ al to 0.16 nucleotide standard deviation was obtained with this system , thus allowing for accurate genotyping of length variants that differ in length by a single nucleotide.