Chapter 18: Autosomal STR Profiling

Regions of the human DNA with an array of tandem repeats

Length of repeat can be 2-6 bp long Microsatellites or Simple Sequence Repeats Most common STR loci: 100-500 bp Advantages of STR loci:

Applicable for PCR amplification Better for degraded DNA Preferential amplification is reduced Better electrophoretic resolution Multiplexing amplification Mixed profiling

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More than 10⁵ STRs in human genome Core repeat region & Flanking regions Repeat Unit Length

Number of nucleotides in a single unit of tandem repeat

Dimeric, Trimeric, Tetrameric, Pentameric, Hexameric

Core repeat Sequences▪ Simple▪ Complex

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Population Match Probability STR loci should be highly variable Loci should not be linked to each other

STR multiplex system in U.K.- 4 loci1995- first national database est. in

U.K. 6 STR loci + amelogenin (4 loci added later)

1997- first database in U.S. CODIS FBI 13 core loci + amelogenin

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European Standard Set (ESS) 1998 7 loci Other: ▪ German database has 8 loci

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Loci are amplified using fluorescent dye-labeled primers

Separated using electrophoresis and detected

Results in an Electropherogram Profile of peaks

Size of STR fragment determined by an internal size standard

Standard curve est.

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Mutations at STR core repeat regionsChromosomal and Gene DuplicationsPoint mutationsAmplification artifacts

Allelic dropout Electrophoretic artifacts

Pull-up Spikes

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Degraded DNA MiniSTR multiplex kits

Low-copy Number DNA (LCN) < 100 pg of DNA

Mixtures Sexual assault cases Mixture interpretation

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SWGDAM & DNA Commission of the ISFG:

Inclusion (Match) Exclusion Inconclusive

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