Forensic Sciences: DNA testing
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Transcript of Forensic Sciences: DNA testing
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Forensic Sciences: DNA testing
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The application of a broad spectrum of sciences to answer questions of interest to the legal system.
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Latent Print analysis Toxicology Crime Scene
Photography Document analysis Blood Spatter analysis Ballistics
Fiber analysis Arson Explosives DNA Computer Other
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Fingerprints Palm prints Footwear and tire impressions Other – ears, lips, etc.
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Used Since? Identification Method Accuracy?
1800 Measurement of height 1 in 4
(Quételet’s method)
Comparison of Pubic hair
1 in 800
Late 1800’s Early 1900’s Comparison of Scalp hair
1 in 4500
Late 1800’s early 1900’s Anthropometry 1 in 268 million
(Bertillon’s method)
Forensic odontologyTeeth bite marks
1 in 2.5 billion
Evidence in Early Egypt – documented forensic use 1800’s -1900’s
Dactylography ?
(Fingerprints)
Late 1900’s DNA Fingerprinting 1 in 2 x 1022
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Restriction Fragment Length Polymorphism (RFLP)
PCR Analysis STR Analysis Mitochondrial DNA Analysis Y-Chromosome Analysis
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•Less than 2% codes for Proteins•50% of the genome contains repeated sequences
•No apparent function•Recombination?•Formation of new genes?
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Restriction Fragment Length Polymorphism
(RFLP)
http://www.youtube.com/watch?v=CfZkn7D6dro
Interactive student in-silico activityhttp://www.pbs.org/wgbh/nova/teachers/body/create-dna-fingerprint.html
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Short Tandem Repeats (STR) are repetitive sequences: Tetranucleotide: AAAG AAAG AAAG AAAG Trinucleotide: CTT CTT CTT CTT CTT Dinucleotide: AG AG AG AG AG AG
Tetranucleotides are favored in human identity Good balance of “ease of interpretation” and
“variability found in nature”
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Original DNA target region
Thermal cycle
Exponential Amplification with PCR
In 32 cycles at 100% efficiency, 1.07 billion copies of amplicon are made.
Thermal cycleThermal cycle
http://www.cstl.nist.gov/div831/strbase/
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Allelic Ladder
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Allele
possibilities
Sample
Genotype
1 in 18
1 locus: 1 in 18 1 in 50X3 loci: 1 in 18000
1 in 20X
2 loci: 1 in 360
Hypothetical likelihood of occurrence
1 in 44X
4 loci: 1 in 792000
9 loci: ~1 in 1010
16 loci: ~1 in 1017
Current World Pop: ~6.3 billion
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Forensic cases: matching suspect with evidence
Paternity testing: identifying father Convicted felon DNA databases Missing persons investigations Mass disasters -- putting pieces back
together Historical investigations Military DNA “dog tag”
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Sources of Biological Evidence
•Blood•Semen•Saliva•Urine•Hair•Teeth•Bone•Tissue
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http://www.cstl.nist.gov/biotech/strbase/intro.htm (some information in this presentation is from this ppt)
http://www.promega.com/applications/hmnid/ (Promega Human identity testing products)
http://www.promega.com/profiles/ (Profiles in DNA)
http://journalsip.astm.org/JOURNALS/FORENSIC/jofs_home.html (Journal of Forensic Science)
http://appliedbiosystems.com Supplier of Human identification systems