Forensic DNA Analysis Genome /04/2015

Forensics “Of, relating to, or denoting the application of scientific methods and techniques to the investigation of crime”

First biological testing in crime  Part of forensic serology  1900: Karl Landsteiner described the ABO blood groups RBC phenotype Reaction with Anti-A Reaction with Anti-B O-- A+- B-+ AB++ Landsteiner et al. 1900

Forensic Processing Workflow Collection of evidence Screenin g for blood, semen, saliva, etc. DNA extraction Quantitation of DNA Amplification of DNA Analysis of DNA Generation of Result

DNA Collection  From crime scene items  Blood, seminal fluid, saliva, epithelial cells, and faeces  Cigarette butts, drinking vessels, bite marks, masks, door handles, steering wheels, knife handles, hair follicles  Reference sample: blood, buccal swabs, pulled hairs An Introduction to Forensic Genetics 2011

Discovery of minisatellites  Alec Jeffreys (1985)  Studying seal myoglobin and discovered the first minisatellite  Human myoglobin gene Jeffreys et al. 1985

Minisatellites  Prone to be in subtelomeric regions of chromosomes  Have core repeat sequence (6 to 100 bp)  Alleles range from 1 kb to 20 kb  Result in multiple alleles

Restriction Fragment Length Polymorphism (RFLP) DNA CS S1 S2 GGGCAGGAXG DNA fingerprinting

Detection of low amounts of DNA  Invention of PCR by Kary Mullis (1983)  Amplification of small quantities of DNA  Focus on microsatellites (short tandem repeats)

Short tandem repeats (STRs)  Throughout the genome  Core unit between 1 and 6 bp  Alleles from 50 to 300 bp  Those used in forensic genetics are tetranucleotide repeats (4) An Introduction to Forensic Genetics 2011

STR analysis PCR 3656 Dye signal Size (nt) Capillary Electrophoresis

Short tandem repeat output  Output for each STR is the repeat count  Easy for storage in databases STRRepeats 110,12 28,13 37,9 48,8 513,14 612,15 77,6

Short tandem repeats (STRs)  Selection criteria for forensics  Discrete and distinguishable alleles  Amplification of locus is robust  High power of discrimination  Absence of genetic linkage with other loci being analyzed  Low levels of artifact during amplification  Ability to be amplified as part of multiplex PCR

Potential Problems

Outcomes of DNA Result  Exclusion (Non-match): Genotype profiles of suspect and crime scene are different  Inconclusive: Genotype profiles can not rule out suspect.  Match (inclusion): Genotype profiles of suspect and crime scene are exactly the same. Statistical significance is assigned to this by a match probability. ( Forensic DNA Typing, 2005

Summary of Techniques Test typeComments RFLP  Requires larger amounts of DNA (micrograms).  DNA must be undegraded. PCR  Requires smaller amounts of DNA than RFLP  Can be somewhat degraded  Extremely sensitive to contamination at crime scene and in crime lab  More prone to error than RFLP  Most often used now due to speed and sensitivity Next generation sequencing  New era arriving in forensic DNA analysis

COmbined DNA Index System (CODIS)  Examines 13 STRs  The National DNA Index (NDIS) contains:  >11,685,829 offender profiles,  1,944,423 arrestee profiles  619,280 forensic profiles  CODIS has produced over 280,451 hits assisting in more than 267,461 investigations.

Profile Applications  Missing persons investigations  Anastasia Romanov – daughter of Tsar Nicholas  All of family except her and her brother were found in a grave  Thought to be missing  Ultimately her and her brother’s remains were discovered in another grave biography.com

Profile Applications  Mass disasters  9/11  As of March 2015: Of 2,753 people reported missing in the attack, remains of 1,113 have never been found

Profile Applications  Paternity  Eddie Murphy and Mel B

First crime solved using DNA forensics Aronson et al. 2005

First crime solved using DNA forensics  1983: Rape and murder of a 15-year old girl (Lydia Mann) in Leicestershire  1986: Nearly identical case in nearby town (Dawn Ashworth)  Police focused on a young kitchen porter with low IQ who ultimately confessed to the second crime DNA from crime scene did not match the kitchen porter DNA Aronson et al. 2005

First crime solved using DNA forensics  ~5,000 men subjected to testing  Blood groups  DNA profiling  Colin Pitchfork avoided the mandatory testing  1987: He was ultimately discovered and convicted of both crimes First crime to exonerate one person and incriminate another using DNA profiling Aronson et al. 2005

Current Efforts  Innocence projecthttp://  As of 4/27/2015  DNA exonerations: 329  Average number of years served: 14  Number of real perpetrators found: 140

Current Efforts