Transcript Forensic Biology by Richard Li - Fayetteville State University

Chapter 18: Autosomal STR Profiling
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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
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STR multiplex system in U.K.- 4 loci
1995- first national database est. in U.K.
 6 STR loci + amelogenin (4 loci added later)
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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
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 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 regions
Chromosomal and Gene Duplications
Point mutations
Amplification artifacts
 Allelic dropout
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Electrophoretic artifacts
 Pull-up
 Spikes
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Degraded DNA
 MiniSTR multiplex kits
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Low-copy Number DNA (LCN)
 < 100 pg of DNA
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Mixtures
 Sexual assault cases
 Mixture interpretation
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SWGDAM & DNA Commission of the ISFG:
 Inclusion (Match)
 Exclusion
 Inconclusive
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