Biology Reference
In-Depth Information
6
The analysis of short
tandem repeats
STRs were first used in forensic casework in the early 1990s [1 - 3]. By the end of the
decade they had become the standard tool for just about every forensic laboratory in
the world. Today the vast majority of forensic genetic casework involves the analysis
of STR polymorphisms and this situation is unlikely to change in the near future [4].
Structure of STR loci
STRs contain a core repeat region between 1 bp
1
and 6 bp long and have alleles
that are generally less than 350 bp long. A large number of STR loci have been
characterized [5] but only around 20 are commonly analysed in forensic casework
(Table 6.1).
The STRs that are widely used in forensic genetics have either a 4 bp or 5 bp
core-repeat motif and can be classified as a simple repeat, simple repeat with non-
consensus repeats, compound repeat or complex repeat [6] (Figure 6.1).
The development of STR multiplexes
The forensic community has selected STR loci to incorporate into multiplex reactions
based on several features including:
•
discrete and distinguishable alleles;
•
amplification of the locus should be robust;
•
a high power of discrimination;
•
an absence of genetic linkage with other loci being analysed;
•
low levels of artefact formation during the amplification (see Chapter 7);
•
the ability to be amplified as part of a multiplex PCR.
1
Note: STRs with repeating core units of 1 bp are not used in forensic analysis.
