How is DNA used to solve crimes? Evidence How is DNA used to solve crimes?

What is DNA? What makes up DNA? DNA stands for deoxyribonucleic acid and contains genetic information. It is found on chromosomes located in the nucleus of our cells. DNA Image: http://science.howstuffworks.com/genetic-science/dna-evidence.htm What makes up DNA? The sides or backbone of the DNA molecule are made up of sugar (deoxyribose) and phosphate molecules. The rungs that form the middle of the molecule are made up of pairs of nucleotides or nitrogen bases. Adenine (A) pairs with thymine (T), while guanine (G) always pairs with cytosine (C). The order of the bases determines the genetic code. Double Helix

Cytosine Adenine Thymine Guanine Backbone Nitrogen (N) Bonds Label the DNA molecule shown below. Word List: Cytosine Adenine Thymine Guanine Backbone Nitrogen (N) Bonds BACKBONE CYTOSINE THYMINE GUANINE ADENINE N BONDS

How is DNA used as evidence? Each person’s DNA is different from other people (except identical twins). DNA collected from a crime scene can either link a suspect to the evidence or eliminate a suspect, similar to the use of fingerprints. DNA can identify a victim through DNA from relatives, even when no body can be found. DNA can link crime scenes together by linking the same perpetrator to different scenes locally, statewide, and across the nation. DNA can place an individual at a crime scene, in a home, or in a room where the suspect claimed not to have been. DNA can refute a claim of self-defense and put a weapon in the suspect's hand. It can change a story from an alibi to one of consent. DNA Strand Image & information : http://www.dna.gov/audiences/investigators/know/

What factors affect DNA evidence? Several factors can affect the DNA left at a crime scene, such as environmental factors (e.g., heat, sunlight, moisture, bacteria, and mold). Therefore, not all DNA evidence will result in a usable DNA profile. Further, DNA testing cannot identify when the suspect was at the crime scene or for how long.   CODIS stands for COmbined DNA Index System, which is an electronic database of DNA profiles that can identify suspects. DNA profiles from individuals convicted of certain crimes, such as rape, murder, and child abuse, are entered into CODIS and help officers identify possible suspects when no prior suspect existed. What is CODIS? Did you know? Each human cell contains three billion DNA base pairs. Our unique DNA amounts to 0.1% or 3 million base pairs. DNA information : http://www.dna.gov/audiences/investigators/know/

Which sets of twins are identical twins? A. Who done it? C. Identical or not? Which sets of twins are identical twins? A. Who done it? Which suspect matches the bloodstain? B. Whose your daddy? Which sample is most likely to be the father? F1 or F2 Information & image from http://www.teachersdomain.org/resource/tdc02.sci.life.gen.lp_dnamysteries/

Which three statements below are true? True or False? Which three statements below are true? 1. The DNA in a man's blood is the same as the DNA in his skin cells and saliva.   2. Each person's DNA is different from every other individual's. 3. DNA can be found in all the cells in our bodies except the blood cells. 4. DNA can have forensic value even if it is decades old. 5. DNA evidence was first used to get a conviction in a trial in 1987. Watch the video segment from NOVA: "The Killer's Trail" and be ready to answer the questions on the next slide. Video available at http://www.teachersdomain.org/resource/tdc02.sci.life.gen.sheppard/ More information available at http://www.pbs.org/wgbh/nova/sheppard/

Choose the best answer for each. Video Quiz Choose the best answer for each. 1. Who was the victim? A. Marilyn Sheppard B. Sam Sheppard C. Sam Sheppard, Jr. 2. What are the keys to DNA fingerprinting? Chromosomes B. Alleles C. Nitrogen bases 3. Where did the scientist get the sample of DNA for Marilyn Sheppard? A. Hair B. Skin C. Fingernail 4. Whose blood was found in the blood trail? A. Marilyn Sheppard B. Sam Sheppard C. Neither

DNA DEOXYRIBONUCLEIC ACID POLYMER MADE OF REPEATING UNITS CALLED NUCLEOTIDES CHROMOSOMES GENES DNA

PARTS OF DNA NUCLEOTIDE 1. SUGAR MOLECULE RIBOSE 2. PHOSPHATE GROUP PHOSPHORUS ATOM SURROUNDED BY 4 OXYGEN ATOMS 3. NITROGEN BASE 4 BASES: ADENINE, THYMINE, GUANINE, CYTOSINE

COMPLEMENTARY BASE PAIRING THE SPECIFIC PAIRING OF BASE A (ADENINE) WITH BASE T (THYMINE) AND BASE C (CYTOSINE) WITH BASE G (GUANINE) IN A DOUBLE STRANDED DNA BECAUSE DNA IS DOUBLE STRANDED THEN YOU MUST HAVE TWO COMPLEMENTARY STRANDS SO…. TTAGGC WOULD BE PAIRED WITH AATCCG AND…. GCGCATAT WOULD BE PAIRED WITH CGCGTATA NOW…YOU TRY IT!

BASE PAIRING PRACTICE 1. TTTACCGA 2. ACCGCTA 3. TTATCGGCA 4. TATATCG 5. CGCGATTA

DNA FINGERPRINTING THE PROCESS OF ISOLATING AND READING DNA MARKERS ESTABLISHES A FINGERPRINT AS UNIQUE AS A PHYSICAL FINGERPRINT IN MANY CASES LINKS BIOLOGICAL EVIDENCE SUCH AS BLOOD, SEMEN, HAIR AND TISSUE TO A SINGLE INDIVIDUAL

REPLICATION: MAKING NEW DNA FROM OLD STEPS OF REPLICATION: DOUBLE STRANDS OF DNA HELIX UNWIND EACH STRAND IS EXPOSED TO FREE NUCLEOTIDES DOUBLE HELIX IS RECREATED BY COMPLEMENTARY BASE PAIRING NEW STRANDS REWIND FORMING TWO DNA MOLECULES POLYMERASES: ENZYMES THAT HELP MAKE AND PROOFREAD NEW DNA STRANDS

ELECTROPHORESIS SEPARATES DNA INTO A “FINGERPRINT” BASED ON THE WEIGHT OF THE DNA SEGMENT STEPS: CUT UP DNA INTO FRAGMENTS USING RESTRICTION ENZYMES USE ELECTRICITY APPLIED TO A GEL TO MAKE THE DNA MOVE ACROSS THE GEL WHICH SORTS IT BY SIZE MOVE FRAGMENTS TO NYLON USING THE SOUTHERN BLOTTING TECHNIQUE TREAT NYLON WITH RADIOACTIVE PROBES PLACE NYLON NEXT TO X-RAY FILM WHICH READS THE RADIOACTIVE PARTICLES DEVELOP THE FILM

Examples of ELECTRPHORESIS FILM

HOW DOES KNOWING HOW DNA WORKS HELP FORENSIC SCIENTISTS? PCR POLYMERASE CHAIN REACTION REPLICATING OR COPYING DNA OUTSIDE OF A LIVING CELL ALLOWS SCIENTISTS TO USE MINISCULE AMOUNTS OF DNA FROM A CRIME SCENE TO RUN REPEATED TESTS

HOW IS DNA COPIED WITH PCR? MUST START WITH A PRIMER: SHORT STRAND OF DNA USED TO TARGET A REGION OF DNA FOR REPLICATION HEAT DNA STRAND TO 94 DEGREES CELCIUS MAKING THEM SEPARATE OR DENATURE ADD PRIMERS TO THE STRANDS AND LET THEM COMBINE LOWER THE TEMPERATURE TO 60 DEGREES CELCIUS ADD DNA POLYMERASE AND FREE NUCLEOTIDES REHEAT TO 72 DEGREES CELCIUS TO TRIGGER REBUILDING OF DNA REPEAT 28-32 TIMES TO GET OVER A BILLION COPIES

ADVANTAGES TO USING PCR CAN BE USED WITH SHORTER DNA STRANDS THAN OTHER METHODS PRODUCES DNA THAT IS MORE STABLE BECAUSE IT IS SMALLER AND NEWER OVERCOMES THE PROBLEM OF LIMITED SAMPLE SIZE OR MINUTE AMOUNTS OF DNA AT A CRIME SCENE

HOW DOES KNOWING HOW DNA WORKS HELP FORENSIC SCIENTISTS? TANDEM REPEATS SECTIONS OF DNA THAT DON’T SEEM TO CODE FOR ANYTHING FILLER MATERIAL REAPEAT OVER AND OVER REPRESENTS OVER 30% OF DNA USED FOR DNA IDENTIFICATION CUZ ITS UNIQUE AND INHERITED SHORT TANDEM REPEATS (STRs) 3-7 REPEATING BASE PAIRS MOST RECENTLY DEVELOPED TEST

ADVANTAGES TO USING STRs SMALLER SEGMENTS THAT ARE EASIER TO WORK WITH LESS LIKELY TO DEGRADE EASIER TO MULTIPLY USING PCR PROCESS THERE ARE 100s OF STRs IN GENES CAN BE SEPARATED USING CAPILLARY ELECTROPHORESIS MULTIPLEXING: TECHNIQUE TO SIMULTANEOUSLY DETECT MORE THAN ONE DNA MARKER IN A SINGLE ANALYSIS

CODIS STRs THERE ARE 13 DIFFERENT STRs IDENTIFIED AND STORED IN THE CODIS SYSTEM GIVES THE PROBABILITY OF AN EVENT OCCURRING BASED ON RACE FOLLOWS THE PRODUCT RULE WHERE YOU MULTIPLY ALL PROBABILITIES TOGETHER TO GET THE OVERALL CHANCE OF AN EVENT

SEX IDENTIFICATION AND STRs GENETICALLY: MALES = XY FEMALES = XX AMELOGENIN GENE: not a STR locus, but it produces X and Y chromosome-specific PCR products of different sizes. FOUND IN TOOTH PULP DIFFERENT LENGTHS IN MALES AND FEMALES Y-STRs: STRs FOUND ONLY ON THE Y CHROMOSOME USED WHEN THERE ARE MULTIPLE MALE SUSPECTS EXAMPLES: RAPE, FIGHTS

MITOCHONDRIAL DNA (mtDNA) DNA IN MITOCHONDRIA ONLY INHERITED FROM MOTHER INFORMATION GATHERED IS USUALLY ONLY BASED ON 2 SEQUENCES (HV1 AND HV2) FIRST USED IN COURT IN 1996, TENNESSEE VS. PAUL WARE RAPE AND MURDER OF 4 YEAR OLD GIRL BASED ON 3 RED HAIRS DEFENSE CLAIMED HE WAS FRAMED BUT THE DNA EVIDENCE WAS AN EXACT MATCH

MITOCHONDRIAL DNA (mtDNA) PROs: MORE SENSITIVE CAN BE OBTAINED FROM A FEMALE RELATIVE IF NONE IS AVAILABLE FROM THE VICTIM/SUSPECT EX. ANASTASIA, MISSING PERSONS CONs: VERY RIGOROUS PROCEDURE TIME CONSUMING EXPENSIVE DOESN’T ELIMINATE FEMALE FAMILY MEMBERS AS SUSPECTS

HANDLING DNA EVIDENCE COLLECTION OF BIOLOGICAL EVIDENCE: Photograph close up Record location at crime scene with notes, photos and sketches Evaluate blood evidence (immediately) On sight overview of crime scene Don’t disturb blood pattern Handel all body fluids and biologically stained materials with minimal personal contact Wear latex gloves and change them frequently All victim and suspect clothing collected and examined Blood should be looked for EVERYWHERE

HANDLING DNA EVIDENCE PACKAGING BIOLOGICAL EVIDENCE: Biological evidence should be packaged in plastic or airtight containers, because accumulation of residual moisture could contaminate and contribute to the growth of bacteria and fungi, destroying it. Articles containing biological evidence should be packaged separately in a paper bag or in a well ventilated box.

HANDLING DNA EVIDENCE OBTAINING DNA REFERENCE SAMPLES: Small objects like toothbrush, razor, hair comb, cigarette butts, and ear plugs - Ex: 9/11 family identification Blood  7mm in a sterile vacuum tube with EDTA in it, must be refrigerated - Ethylenediamine tetraacetic acid (EDTA) is a preservative that inhibits the activity of enzymes that degrade DNA Buccal swab  cotton swab placed in mouth, swab inside of cheek, transfers buccal cells onto swab

HANDLING DNA EVIDENCE CONTAMINATION OF DNA EVIDENCE: Can occur by introducing foreign DNA during the collection process (coughing, sneezing). Transfer of other foreign DNA when items of evidence are incorrectly placed next to each other. TO MINIMIZE CONTAMINATION: -change gloves before handling new evidence. -collect substrate control for examination. -pickup small evidence with clean tools. -package items in own container.