Investigating CSI – Background material Table of Contents I ...

Short Tandem Repeat (STR) Analysis
Short tandem repeat (STR) technology is used to evaluate specific regions (loci)
within nuclear DNA. Variability in STR regions can be used to distinguish one
DNA profile from another. STR loci consist of short, repetitive sequence
elements 3 to 7 base pairs in length . These repeats are well distributed
throughout the human genome and are a rich source of highly polymorphic
markers, which may be detected using the polymerase chain reaction (5–8).
Alleles of STR loci are differentiated by the number of copies of the repeat
sequence contained within the amplified region and are distinguished from one
another using radioactive, silver stain or fluorescence detection following
electrophoretic separation.
One system, The PowerPlex® 16 System, allows the coamplification and threecolor
detection of sixteen loci (fifteen STR loci and Amelogenin). The loci are
grouped into three different group, each group labeled with a different compound
(fluorescein, JOE, and TMR) that will fluoresce either green, red, or blue. The
labeling occurs during PCR amplification of the DNA.
All sixteen loci are amplified simultaneously in a single tube and analyzed in a
single injection or gel lane. For more details, see below.
The Promega PowerPlex 16 system:
The fluorescein-labeled allelic ladder showing all possible repeat lengths in each
STR loci. The numbers on the ruler at the top (100-480) represent the number of
base pairs and the overall region where the loci is located. The boxes just blow
the ruler show the names of each loci. The peaks show all possible peaks for
each loci and the boxed in numbers below the peaks show the number of repeats
in each peak represents.
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