Forensic Analysis of DNA
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Transcript of Forensic Analysis of DNA
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Forensic Analysis of
DNAChapter 9
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DNA
Genetic Material Double stranded; two strands of nucleotides http://www.youtube.com/watch?v
=ZGHkHMoyC5I Nucleotides have phosphate group, deoxyribose
sugar, and nitrogenous base (adenine, thymine, guanine, and cytosine)
DNA is copied into new DNA through DNA replication in nucleus
http://www.youtube.com/watch?v=teV62zrm2P0 DNA is transcribed into mRNA in nucleus; mRNA
is converted to proteins through translation at the ribosome
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DNA Replication
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Transcription—DNA to mRNA
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Restriction Enzymes
Cut DNA has specific recognition sequence
Extracted from bacteria Gives fragments of different sizes http://www.youtube.com/watch?v=
lPdQwdGgyfQ
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Restriction Enzymes
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Polymerase Chain Reaction
Makes many copies of small collected DNA samples
Done prior to other testing Uses DNA polymerase, 2 kinds of primers,
free nucleotides, and thermal cycler Uses heating to denature and cooling for
annealing Can get 2n DNA double helices where n is
the number of heating and cooling cycles http://www.youtube.com/watch?v
=v4L7rvmBXbY
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PCR
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Repetitive DNA
When during DNA typing, want to use non-coding repetitive DNA; not coding DNA
Much more variation in non-coding DNA Tandem repeats; non-coding repetitive DNA VNTR—variable number tandem repeats;
often used for DNA typing STR—short tandem repeats; used most
often for DNA typing RFLP—restriction fragment length
polymorphism; cut with restriction enzymes to make many fragments
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VNTR
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STR
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STR
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RFLP
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Electrophoresis
Load negative DNA at black side of chamber into gel (agarose or polyacrylamide)
DNA moves to positive electrode Small fragments move farther through
the gel Buffer is used as electrolyte to help
send current through gel http://www.youtube.com/watch?v
=0x2Lh5Rq8e0&feature=related
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Electrophoresis
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DNA Typing--Identification
http://www.youtube.com/watch?v=RCI9YhstHK4&feature=fvw
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Crime Scene DNA Analysis
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DNA Typing—Paternity Testing
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Paternity Testing
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Paternity Testing
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Hybridization
DNA from electrophoretic gel is transferred to nylon membrane or paper filter
DNA can be heated to be denatured Radioactive or fluorescent probe are
used to find specific DNA section
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Hybridization
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DNA Typing
Amplify with PCR Use restriction enzymes to make RFLPs
of STR or VNTR sequence of genome Separate fragments with
electrophoresis Match bands with known samples to
determine identity Can be used for crime scene matching,
paternity testing, and identifying corpses or body parts
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CODIS
STR data for first 13 STRs are put into CODIS
If use at least 6 STRs, matching process is very precise; 1 in 2,000,000 probability; Using all 13 makes the probability of an incorrect match being 1 in 575-900 trillion
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CODIS STRs
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Capillary Electrophoresis
Use glass capillary tube with gel wrapping and buffer reservoir
STRs move through column and as pass through column peak appears on attached computer instrument
Peak diagram is called an electropherogram
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STR used for gender identification
Uses amelogenin gene whose length is different in X and Y chromosome
STR electrophoresis shows two separate bands for presence of X and Y chromosome in males
Shows one band for 2 X chromosomes in females
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Gender ID with STR
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mtDNA
Found outside nucleus is mitochondria Easier to get and can be taken from
any relative of the same maternal lineage
Same in all relatives from same maternal line; so not as specific of a match
Can be gotten when burning, age, or environmental degradation has damaged genomic DNA
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Mitochondrial DNA
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DNA sources for collection
Any cells from skin, in blood, cheek cells from saliva, epithelial cells in hair follicles
Sweat, semen, ear war, mucus can also be used to extract cells for DNA typing
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Collection of Biological Evidence
Photograph, sketch, describe, and collect
Collect from body fluids, tissues, trash, laundry, placed often touched (handles, light switches; places licked (envelopes, lipstick, cigarettes, partially eaten food for drink); places where body fluids might be (clothing, tissues, sheets, pillows, condoms)
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DNA Evidence
Package each DNA stained item separately in paper bag or well-ventilated container; closed containers can lead to moisture and growth of DNA digesting bacteria
Obtain reference DNA—buccal cells or blood
Avoid contamination—wear gloves; never cross-contaminate DNA from one piece of evidence with another; use different instruments for every piece of evidence