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