DNA Fingerprinting and Forensic Analysis Lecture 21 IHC / T.M.A Dep. DNA Fingerprinting and Forensic Analysis

Introduction to DNA Fingerprinting and Forensics Forensic science – intersection of law and science Historic examples 1800s – photography Early 1900s – fingerprints DNA Fingerprinting – 1985 Unique signature found in each person’s genetic makeup

What Is a DNA Fingerprint? Every individual carries a unique set of genes Chemical structure of DNA is same, but the order of the base pairs differs Every cell contains a complete set of DNA that identifies the organism as a whole Only one tenth of 1% of DNA differs from person to person

What Is a DNA Fingerprint? Two Main Types of Forensic DNA Testing RFLP (restriction fragment length polymorphism) Requires larger amounts of DNA DNA cannot be degraded PCR (polymerase chain reaction) Less DNA and DNA can be partially degraded Extremely sensitive to contaminating DNA

What Is a DNA Fingerprint? DNA profiling depends on a small portion of the genome Exons code proteins Introns do not code for proteins The introns contain repeated sequences of between 1 and 100 base pairs Called variable number tandem repeats (VNTR’s) Some VNTR’s are inherited from mother and some from father

What Is a DNA Fingerprint?

Preparing a DNA Fingerprint

Preparing a DNA Fingerprint

What Is a DNA Fingerprint? DNA fingerprinting is restricted to the detection of microsatellites 1 to 6 nucleotide repeats dispersed throughout the chromosomes Probes used to identify the microsatellite surround the specific microsatellite being analyzed Also called short tandem repeats (STR) FBI has chosen 13 unique STRs for testing Combined DNA Index System (CODIS)

Y-Chromosome STR Profile Y-STRs can permit simplification of male DNA identification in sexual assault cases Female Victim DNA Profile Male Perpetrator DNA Profile DNA Profile from Crime Scene No signal observed Figure 9.2 Schematic illustrating the types of autosomal or Y-STR profiles that might be observed with sexual assault evidence where mixtures of high amounts of female DNA may mask the STR profile of the perpetrator. Y-STR testing permits isolation of the male component without having to perform a differential lysis. Autosomal STR Profile Y-Chromosome STR Profile Butler, J.M. (2005) Forensic DNA Typing, 2nd Edition, Figure 9.2, ©Elsevier Science/Academic Press

Steps in Forensic DNA Analysis Collection Extraction Quantitation STR Typing Interpretation of Results Database Storage & Searching Specimen Storage Multiplex Calculation of Match Probability Steps Involved Usually 1-2 day process (a minimum of ~5 hours) DNA Quantitation Slot Blot 1 ng 0.3 ng 0.7 ng 0.5 ng No DNA Sample Collection & Storage Buccal swab Blood Stain DNA Extraction Biology Multiplex PCR Amplification If a match occurs, comparison of DNA profile to population allele frequencies to generate a case report with probability of a random match to an unrelated individual Genetics STR Typing DNA separation and sizing DNA Database Search Technology Male: 13,14-15,16-12,13-10,13-15,16 Interpretation of Results

PowerPlex Y Performance in Our Hands 2 ng male 2 ng male: 15 ng female 500 pg male: 408 ng female 800X female DNA 1 ng male: 816 ng female

Short Tandem Repeat (STR) Typing Fluorescent dye-labeled primer Short Tandem Repeat (STR) Typing STR Repeat Region 3′ 5′ (Maternal) 1 2 3 4 5 6 3′ 5′ (Paternal) 1 2 3 4 5 6 7 8 GATA forward primer hybridization region reverse primer hybridization region 75….80….100….120….140….160….180….200….220….240.…260….. (size in bp) RFUs 1000 500 6 139bp 8 147bp DNA Separation and Detection

PATERNITY TESTING Family Inheritance of STR Alleles (D13S317) 11 14 PCR product size (bp) 11 14 Father 12 14 Child #1 8 14 Child #2 11 12 Child #3 8 12 Mother

Famous Cases Colin Pitchfork was the first criminal caught based on DNA fingerprinting evidence. He was arrested in 1986 for the rape and murder of two girls and was sentenced in 1988.

Famous Cases O.J. Simpson was cleared of a double murder charge in 1994 which relied heavily on DNA evidence. This case highlighted lab difficulties.

Famous cases In 2002 Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father of her child Damien