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History and Development of Commercial Short Tandem Repeat (STR) Kits for Forensic DNA Analysis in the United Kingdom
Introduction
Short Tandem Repeat (STR) profiling is the backbone of modern forensic DNA analysis in the United Kingdom. It allows investigators to identify individuals based on variations in repeated DNA sequences that are highly variable between people. Since its introduction in the 1990s, STR technology has developed from early in-house systems to highly standardised commercial multiplex kits used globally.
This essay traces the historical development of STR profiling in the UK, focusing on key transitions in marker selection, the increasing number of loci used, and the compatibility of STR systems with challenging forensic samples. It also critically evaluates the strengths and limitations of these developments in forensic practice.
Early Development of Forensic DNA Profiling in the UK
Forensic DNA analysis in the UK began in 1986 with DNA fingerprinting developed by Sir Alec Jeffreys. However, early methods based on Variable Number Tandem Repeats (VNTRs) were time-consuming and required high-quality DNA, limiting their forensic use.
The real shift came in the 1990s with the adoption of PCR-based STR analysis. STRs were much shorter DNA regions, making them suitable for degraded samples and enabling rapid amplification. The UK’s Forensic Science Service (FSS) played a central role in developing early STR systems, particularly the SGM (Second Generation Multiplex) system introduced in 1995.
SGM initially used six STR loci plus a sex-typing marker (amelogenin). This marked the beginning of standardised forensic DNA profiling in the UK.
Development of SGM Plus and Expansion of STR Markers
The SGM system was later upgraded to SGM Plus in 1999. This expanded the number of STR loci to ten core markers. This development significantly improved discrimination power, reducing the probability of random match and increasing confidence in forensic identifications.
SGM Plus became the standard system used in the UK National DNA Database (NDNAD) for many years. It included highly polymorphic STR loci such as D3S1358, VWA, and FGA, which provided strong statistical power for individual identification.
The choice of markers in SGM Plus was carefully considered. Loci were selected based on:
- High variability in human populations
- Independence (low linkage between loci)
- Reliable amplification in PCR
- Compatibility with degraded DNA
However, early systems were still limited in dealing with complex mixtures and highly degraded samples, which became increasingly important in forensic casework.
Transition to Commercial STR Kits
From the early 2000s, forensic laboratories in the UK began shifting from in-house developed systems to commercially produced STR kits. Companies such as Applied Biosystems and Promega developed standardised multiplex kits like Identifiler and PowerPlex.
This transition was significant because commercial kits offered:
- Greater standardisation across laboratories
- Improved quality control
- Higher multiplex capacity (more loci per reaction)
- Better sensitivity and automation compatibility
These kits also aligned UK profiling more closely with international systems, particularly those used in Europe and the United States.
Expansion to European Standard Set (ESS) and Beyond
A major development in STR profiling was the adoption of the European Standard Set (ESS). Initially, this included 7 core loci, later expanded to 10 and then 12 loci. The aim was to improve interoperability between European DNA databases.
The UK National DNA Database aligned with ESS requirements, ensuring that profiles could be compared across jurisdictions.
More recently, STR kits have expanded further to include 20 to 24 loci, such as in GlobalFiler and PowerPlex Fusion systems. The UK adopted expanded marker sets as part of the move towards the expanded ESS (eESS), improving discrimination power significantly.
These modern systems include additional rapidly mutating loci and quality control markers, which enhance performance in complex forensic scenarios.
