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DNA Types of evidence and how they are tested for DNA 2009©Forensic Science Today Alec Jeffries Asked to determine paternity Child wanting to immigrate Was he related? See also Audri Kowalyk, Introductory Forensic Science Educational Activities, Unit 7 History is Made: First Crime Solved Using DNA 2009©Forensic Science Today First Criminal Case DNA first used in Colin Pitchfork case, 1988. 3 villages were “sampled”, approx 5000 men. Also exonerated Richard Buckland. (See handout from Kowalyk, History Is Made. . Lynda Mann/Dawn Ashcroft rape & murder case) 2009©Forensic Science Today Examples Anastasia and Tsar Nicholas Egyptian Mummies Paternity Larry Hillblom Courier company DHL Young girls Children 2009©Forensic Science Today Deoxyribonucleic Acid Genetic make-up for every person is unique. Inherit half from your mother and half from your father. Half can be any combination of that parent’s alleles. An allele is a single coding on a location on your DNA A gene is made of a pair of alleles 2009©Forensic Science Today DNA – The Basics First discovered in 1868 1950’s- James Watson & Francis Crick deduced the structure of DNA DNA is a polymer composed of repeating units called nucleotides. Nucleotide is made up of a sugar molecule, a phosphorus-containing group and a nitrogencontaining base. Bases are adenine, thymine, guanine, cytosine 2009©Forensic Science Today DNA Structure http://nobelprize.org/educational/medicine/dna_double_helix/readmo re.html James Watson – Left Francis Crick - Right 2009©Forensic Science Today Complementary Base Pairing A - T and G – C base pairs only No restrictions on sequencing Average human chromosome has 100 million base pairs 2009©Forensic Science Today What is DNA Found In? Found in these parts of your body materials Blood Saliva Skin cells Sperm 2009©Forensic Science Today DNA Can Be Found On.. Can be left in the following types of evidence Anything that rubs against skin laundry, hats, bed clothes, glasses Anything that you breathe on bandana, mask, tissue Anything you exchange saliva with toothpick, cigarette, drink container, stamp, envelope, toothbrush, bite mark etc. Anything you “exchange” skin cells with other person’s fingernails, watch bands, tape stuck on you, fecal matter Anything you exchange body fluids with condoms, bullets that travel through the body 2009©Forensic Science Today Where is DNA Found in the Cell? The nucleus In the form of chromosomes A very long DNA molecule containing the nucleotide sequence (genetic code) Inherited from both parents Humans have 46 chromosomes (23 pairs) Sex chromosomes (XX in females, XY in males) 2009©Forensic Science Today Where is DNA Found in the Cell? The mitochondria Smaller than nuclear DNA Inherited from a person’s mother Mitochondrial DNA produces enzymatic proteins that function to convert energy into a usable form within the cell. mtDNA is constructed in a circular or loop configuration. See Figure 13-17, p. 388, p. 389 Law Enforcement Bulletin 2009©Forensic Science Today 2009©Forensic Science Today Nuclear vs. Mitochondrial DNA in Forensic Identification Nuclear DNA is more informative Cell contains one nucleus but thousands of mitochondria. Mitochondrial DNA lasts longer and is more easily extracted from degraded samples such as ancient bones. A mtDNA reference sample can be obtained from any maternally related relative Forensic analysis of mtDNA is more rigorous, time consuming and costly than nuclear DNA profiling 2009©Forensic Science Today Nuclear DNA Nuclear DNA has been used to determine the descendants of Thomas Jefferson Nuclear DNA determines paternity in child custody cases 2009©Forensic Science Today Nuclear DNA Findings Nuclear DNA has been used to analyze the genetic qualities of Egyptian mummies 2009©Forensic Science Today Discoveries from Mitochondrial DNA Used to test charred remains of Tsar Nicholas and his family who were executed during the Russian revolution of the early 20th century 2009©Forensic Science Today Steps Involved in the Examination of Evidence for DNA- Extraction Possible sources of DNA are body tissue, organs, root of hair, bodily fluids or bone Chain of custody must be maintained! Each sample must be handled with a clean pair of gloves or disposable forceps. Samples should be kept cold and stored in a freezer. Wet or liquid samples should be air-dried. 2009©Forensic Science Today Steps Involved in the Examination of Evidence for DNA-Analysis by RFLP Restriction Fragment Length Polymorphisms First accepted analytical method for DNA used in the U.S. Must have nickel sized sample to test Tests for patterns that occur by cutting the DNA using specific enzymes. When the cut is made, the sections are separated by their size, using electrophoresis. (See pp. 135-136, Figure 13-9, p. 373) Can give results that are relatively unique Can not use degraded DNA Used in the impeachment trial of President Bill Clinton to identify the semen stain on Monica Lewinsky’s dress. See p. 374 Technology has been phased out. Replaced by PCR. 2009©Forensic Science Today • Contributed by Harold Messler, Manager of the St. Louis Metropolitan Police Department Crime Lab 2009©Forensic Science Today Steps Involved in the Examination of Evidence for DNA- Amplification Use of Polymerase Chain Reaction (PCR) to copy a small sample of DNA. Sample may be degraded. Prevention of false results requires carefully applied controls and technique. Cross contamination with known DNA must be avoided. Sample is placed in a thermal cycler with a mixture of nucleotides and DNA replication enzyme (DNA polymerase) See p. 367 Figure 13-5 High temperatures (94ºC) cause the DNA helix to separate. (denaturation) DNA copies itself using the nucleotides and DNA polymerase. (See pp. 372-376) Separation & duplication process is repeated 28-30 times. 2009©Forensic Science Today DQ-alpha PCR Contributed by Harold Messler, Manager of the St. Louis Metropolitan Police Department Crime Lab 2009©Forensic Science Today Steps Involved in the Examination of Evidence for DNA-Comparison of STR Markers* Samples as small as a few cells Works for very degraded samples Uses PCR technique to amplify sample Looks at 13 specific STR regions (p. 379 Table 13-1) An example of an STR is D7S280, it is found on human chromosome 7. The sequence GATA is repeated within this loci. Different individuals have different numbers of repeats at these loci Used to create DNA profiles for databases-a dozen or more matching STR markers constitutes a match 2009©Forensic Science Today Image provided by Promega Corporation. See www.promega.com for more information. 2009©Forensic Science Today Single Nucleotide Polymorphisms SNPs An alteration in a gene that occurs in at least 1% of the population. Need at least 50 SNPs to give same results as 13 STR sites. 2009©Forensic Science Today SNP Example SNPs, typed for 70 non-sex genetic markers Go to the following website for an example of an SNP and information about them. http://www.dna.gov/research/alternative_markers/autosomalsnps 2009©Forensic Science Today DNA Results Must be explained in relation to statistical probability. Since the entire DNA is never tested, DNA technicians should not say that the results can match only one person. Instead, they explain the probability of another person matching these results. 2009©Forensic Science Today Protect evidence Prevent damage before collection Do not move unless it is a high risk of loss. If you must move the evidence, carefully document its location and the action you are taking. Note location and description of evidence 2009©Forensic Science Today Collection of DNA Evidence Change gloves between each piece of evidence collected to prevent crosscontamination Do not collect in plastic. If not dry, molding can occur which will degrade the DNA Collect in separate containers, properly labeled and sealed 2009©Forensic Science Today Collection continued Sexual assault evidence on victim Protect the evidence by loosely wrapping victim in clean sheet while transporting victim to hospital for sexual assault examination Always collect evidence in paper containers unless the evidence can tear the container Air-dry evidence before collection, when possible. 2009©Forensic Science Today Protecting DNA Must be kept cold, -80oF Must not expose it to your DNA by touching it (skin to sample) or breathing, coughing or sneezing on it. 2009©Forensic Science Today Types of DNA Databases Sex Offender Felony Offender Felony Arrest All Type Arrest Total 1,407,000 DNA Profiles in the U.S. CODIS database and 64,500 in the forensic database. 2009©Forensic Science Today CODIS Combined DNA Index System National database of DNA STR test results handled by the FBI Collected from crime scene samples, convicted persons. Contains samples from solved and unsolved crimes 2009©Forensic Science Today Offender Hits at State DNA Index System (SDIS) Through May 2004 8,949 Offender Hits in 42 States and 2 Federal Laboratories 96 238 35 2 8 90 2 329 4 1 1 30 11 508 83 44 161 75 337 187 47 24 239 1715 75 113 (MA) 1516 340 7 50 (CT) 18 (NJ) 54 (MD) 20 (FBI lab) 47 37 33 295 38 266 270 2 (US Army) 122 20 1360 Hawaii 2009©Forensic Science Today Puerto Rico