Forensic Analysis of DNA Chapter 9. DNA Genetic Material Double stranded; two strands of...
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Transcript of Forensic Analysis of DNA Chapter 9. DNA Genetic Material Double stranded; two strands of...
Forensic Analysis of
DNAChapter 9
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
DNA Replication
Transcription—DNA to mRNA
Restriction Enzymes
Cut DNA has specific recognition sequence
Extracted from bacteria
Gives fragments of different sizes
http://www.youtube.com/watch?v=lPdQwdGgyfQ
Restriction Enzymes
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
PCR
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
VNTR
STR
STR
RFLP
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
Electrophoresis
DNA Typing--Identification
http://www.youtube.com/watch?v=RCI9YhstHK4&feature=fvw
Crime Scene DNA Analysis
DNA Typing—Paternity Testing
Paternity Testing
Paternity Testing
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
Hybridization
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
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
CODIS STRs
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
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
Gender ID with STR
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
Mitochondrial DNA
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
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)
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