Forensic Biology by Richard LiBasicsCharacteristics of STR LociSTR Commonly UsedSlide 5Forensic STR AnalysisFactors Affecting Genotyping ResultsGenotyping of Challenging Forensic SamplesInterpretation of ResultsChapter 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 profilingForensic Biology by Richard Li 2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▪ComplexForensic Biology by Richard Li 3Population Match ProbabilitySTR loci should be highly variableLoci should not be linked to each otherSTR multiplex system in U.K.- 4 loci1995- 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 + amelogeninForensic Biology by Richard Li 4European Standard Set (ESS)19987 lociOther: ▪German database has 8 lociForensic Biology by Richard Li 5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.Forensic Biology by Richard Li 6Mutations at STR core repeat regionsChromosomal and Gene DuplicationsPoint mutationsAmplification artifactsAllelic dropout Electrophoretic artifactsPull-upSpikesForensic Biology by Richard Li 7Degraded DNAMiniSTR multiplex kitsLow-copy Number DNA (LCN)< 100 pg of DNAMixturesSexual assault casesMixture interpretationForensic Biology by Richard Li 8SWGDAM & DNA Commission of the ISFG:Inclusion (Match)ExclusionInconclusiveForensic Biology by Richard Li