"DE isenberg Part 1"
Genetic Statistic Application in Forensic Science Arthur J. Eisenberg, PhD Professor and Chairman Department of Forensic and Investigative Genetics Co-Director UNT Center for Human Identification Institute of Investigative Genetics University of North Texas Health Science Center Fort Worth, Texas USA The Science of DNA for Human Identification DNA is Responsible for Transmitting Hereditary Characteristics Human Cells Contain Two Kinds of DNA Nuclear DNA and Mitochondrial DNA * * The Nucleus Contains 23 Pairs of Chromosomes DNA in the Cell Target Region for PCR DNA Amplification with the Polymerase Chain Reaction (PCR) 5’ 3’ 5’ 3’ Starting 3’ 5’ DNA 3’ 5’ Template Separate strands (denature) Forward 5’ primer 3’ 5’ 3’ Make copies Add primers (extend primers) 3’ 5’ 3’ 5’ (anneal) Reverse primer PCR Copies DNA Exponentially through Multiple Thermal Cycles Original DNA target region Thermal cycle Thermal cycle Thermal cycle In 32 cycles at 100% efficiency, 1.07 billion copies of targeted DNA region are created 13 CODIS Core STR Loci TPOX D3S1358 D8S1179 TH01 D5S818 VWA FGA D7S820 CSF1PO AMEL D13S317 AMEL D18S51 D16S539 D21S11 Alleles – Contain Varying Numbers of 4 Base Pair Repeats Allele: 5 AATG AATG AATG AATG AATG 6 AATG AATG AATG AATG AATG AATG 7 AATG AATG AATG AATG AATG AATG AATG Flanking region of unique sequence Typical DNA Profile D3S1358 14,16 D13S317 11,12 vWA 14,19 D7S820 10,10 FGA 21, 21 D16S539 12,13 D8S1179 11,15 THO1 7, 9 D21S11 30, 32 TPOX 8,12 D18S51 15,17 CSF1PO 11,13 D5S818 12,12 Ameloginin X,Y Multiplex PCR • Over 15 Markers Can Be Copied at Once • Sensitivities to levels less than 1 ng of DNA • Ability to Handle Mixtures and Degraded Samples • Different Fluorescent Dyes Used to Distinguish STR Alleles with Overlapping Size Ranges 310 Genetic Analyzer Capillary Electrophoresis Current CODIS Acceptable Kits AmpFlSTR® Identifiler™ D8S1179 D21S11 D7S820 CSF1PO 6FAM (blue) TH01 D3S1358 D13S317 D16S539 VIC D2S1338 (green) TPOX D19S433 VWA D18S51 NED (yellow) AMEL D5S818 FGA PET (red) GS500 LIZ size standard LIZ (orange) Current CODIS Acceptable Kits COMBINED DNA INDEX SYSTEM CODIS MISSION • The FBI Laboratory's Combined DNA Index System (CODIS) blends forensic science and computer technology into an effective tool for providing investigative leads to assist in solving crimes. • CODIS enables federal, state, and local crime labs to exchange and compare DNA profiles electronically, thereby linking crimes to each other and to convicted offenders, as well as in the identification of missing persons and human remains. What is a Database? A database is an organized file or files of data that can be searched to retrieve information DNA databases compare crime scene evidence to a database of DNA profiles obtained from known individuals to provide the Police with investigative leads CODIS ARCHITECTURE NDIS National California Florida Texas SDIS CalDOJ FDLE DPS LDIS LDIS LDIS LDIS Tampa, FL Tallahassee, FL Orlando, FL CODIS INDICES OFFENDER Convicted Offenders Arrestee FORENSIC Forensic Crime Scene Samples MISSING PERSONS • Unidentified Human Remains • Missing Persons Direct Reference Samples (baby teeth, tooth brush, hair brush, etc.) • Family Reference Samples Question 1 How common or rare is the evidence profile? • This can be calculated by either the random match probability (RMP) or by using the likelihood ratio (LR) using the Hardy-Weinberg Equilibrium Formula. p12 + 2p1p2 + p22 = 1 A1A 1 = p 12 A1A2 = 2p1p2 A2A2 = p 22 freq(A1) = p1 freq(A2) = p2 For homozygous loci, a Theta correction () is used to account for population substructure Homozygous locus frequency = p2+p(1-p) PART 2 Paternity Exclusion Dual Obligate allele Obligate alleles Obligate allele X X X Paternity Exclusion Obligate allele Obligate allele Obligate allele Obligate allele X X X X Paternity Exclusion Dual Obligate alleles Obligate allele X X Paternity Inclusion Obligate allele Obligate allele Obligate allele Obligate allele Obligate allele Paternity Inclusion Dual Dual Obligate allele Obligate alleles Obligate allele Obligate allele Obligate alleles Obligate allele Paternity Inclusion Obligate allele Obligate alleleObligate allele Obligate allele If the Alleged Father Cannot be Excluded Several Statistical Values are Calculated to Assess the Strength of the Genetic Evidence PI Paternity Index CPI Combined Paternity Index W Probability of Paternity PE Probability of Exclusion Paternity Index • Summarizes the genetic information provided by the DNA analysis of the Mother, the Child, and the Alleged Father • The Numerator is the Probability of observing the genetic results for the three individuals tested under the assumption that they are a true trio • The Denominator is the probability of observing the same genetic results for the three individuals under the assumption that they are a false trio. Probability of Paternity • The probability of paternity is a measure of the strengths of one’s belief in the hypothesis that the tested man is the father. • The correct probability must be based on all of the evidence in the case. • The non-genetic evidence comes from the testimony of the mother, tested man, and other witnesses. • The genetic evidence comes from the DNA paternity test. Probability of Paternity • The prior probability of paternity is the strength of one’s belief that the tested man is the father based only on the non-genetic evidence. • P = Prior Probability; it is a number greater than 0 and less than or equal to 1. In many criminal proceedings the Probability of Paternity is not admissible. • In criminal cases, the accused is presumed innocent until proven guilty. Therefore, the defense would argue that the Prior Probability should be 0. You cannot calculate a posterior Probability of Paternity with a Prior Probability of 0. Probability of Paternity • In the United States, the civil court system has made the assumption that the prior probability is equal to 0.5. • The argument that is presented is that the tested man is either the true father or he is not. In the absence of any knowledge about which was the case, it is reasonable to give these two possibilities equal prior probabilities. DNA Paternity Testing • No test available can prove with a probability of paternity or maternity of 100% that a man or woman is the biological parent of a child. • Currently available DNA testing will routinely provide greater than a 99.9999% probability of paternity/maternity when the biological mother is tested in conjunction with the child and the alleged father. This is in excess of the 99% or 99.9% requirement of most U.S. civil courts. Probability of Exclusion • The probability of exclusion (PE) is defined as the probability of excluding a random individual from the population given the alleles of the child and the mother. • The genetic information of the tested man is not considered in the determination of the probability of exclusion • The probability of exclusion (PE) is equal to the frequency of all men in the population who do not contain an allele that matches the obligate paternal allele of the child. PART 3 Arthur J. Eisenberg, PhD Professor and Chairman Dept of Forensic and Investigative Genetics Co-Director UNT Center for Human Identification Institute of Investigative Genetics University of North Texas Health Science Center Fort Worth, Texas USA 817 735-0555 Arthur.firstname.lastname@example.org