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Chapter8DNAFingerprintingandForensicAnalysis.ppt

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Chapter8DNAFingerprintingandForensicAnalysisWhatisaDNAfingerprint?Howdowedistinguishoneperson’sDNAfromanother?STRsTheuniquenessofanindividual’sSTRsprovidesthescientificmarkerofidentityknownasaDNAfingerprint. IntheUnitedStatestheFBIhasstandardizedasetof13STRassays(13differentlocationsonthechromosomes)forDNAtyping,andhasorganizedtheCODISdatabaseforforensicidentificationincriminalcases. TheUnitedStatesmaintainsthelargestDNAdatabaseintheworld:TheCombinedDNAIndexSystem,withover60millionrecordsasof2007. PreparationofaDNAfingerprintStep1DNAfingerprintingisacomparativeprocess: DNAfromcrimesceneiscomparedwithDNAofasuspect Sominimumoftwosamplesmustbeprepared Step2 DNAextraction standardizedmethodshavebeendeveloped needtoseparateDNAfromothercellmaterialanddebrisfromcrimescene.Step3PCRusingprimerstargetingSTRsatdifferentlociStep3PCRamplificationofDNAPCRallowsyoutomakemillionsofcopiesoftheSTRregionfromasinglecopyofDNAyourecoveredfromcrimescene. Sincethe#oftimessequenceisrepeatedisdifferentforeachperson,fragmentsizewillbedifferent. Thisisdonefor13differentSTRsequencesatthisonelocus Differencesoccuramongindividualsateachofthe13locionthechromosomewheretheSTRsoccur Thisallowsforalotofvariation RestrictionFragmentLengthPolymorphismIfyoudothisfor13differentrepeatsequencesat13differentlocionthechromosome,eachpersonproducesadifferentbandpatternwhenthefragmentsareseparatedbygelelectrophoresisDifferentSTRsatotherlociOtherapproachestoDNAfingerprintingDotblotting(continued) BecauseeverygeneamplifiedbyPCRhasthesamelength,wedon’tneedtouseelectrophoresistosortandseparatethefragments. Instead,weuse“blotstrip”ordotblotwhichcontainsadifferentDNAprobethatissensitivetothesequencevariability.DotBlotBindingofprobetocomplementaryDNAWashawayunreactedprobeandaddbiotin-reactiveenzymeDotBlotWhatdoweendupwith?DNAfingerprintinginpracticeTransfercellsonswabtolysisbuffer1AlwaysneedsuspectDNANeedluckybreakoraleadthatgetsyoutotheperpetratororthecrime. DNAprofiledatabaseInvasionofprivacyDNAfingerprintcanbeu