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

Make copies (extend primers) Starting DNA Template 5’ 3’ 5’ 3’ Add primers (anneal) 5’ 3’ 5’ Forward primer Reverse primer Separate strands (denature) 5’ 3’ DNA Amplification with the Polymerase Chain Reaction (PCR)

In 32 cycles at 100% efficiency, 1.07 billion copies of targeted DNA region are created PCR Copies DNA Exponentially through Multiple Thermal Cycles Original DNA target region Thermal cycle

13 CODIS Core STR Loci CSF1PO D5S818 D21S11 TH01 TPOX D13S317 D7S820 D16S539 D18S51 D8S1179 D3S1358 FGA VWA AMEL

Alleles – Contain Varying Numbers of 4 Base Pair Repeats

Typical DNA ProfileD3S135814,16D13S31711,12 vWA14,19D7S82010,10 FGA 21, 21 D16S53912,13 D8S117911,15THO1 7, 9 7, 9 D21S11 30, 32 TPOX 8,12 8,12 D18S5115,17CSF1PO11,13 D5S81812,12AmelogininX,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

D8S1179 D21S11 D7S820 CSF1PO D3S1358 TH01 D13S317 D16S539 D2S1338 D19S433 D18S51 TPOX VWA AMEL D5S818 FGA GS500 LIZ size standard 6FAM (blue) VIC (green) NED (yellow) PET (red) LIZ (orange) AmpFlSTR ® Identifiler™

Current CODIS Acceptable Kits

COMBINED DNA INDEX SYSTEM

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. CODIS MISSION

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 National LDIS Tampa, FL LDIS Tallahassee, FL FDLE CalDOJ LDIS Orlando, FL DPS NDIS SDIS LDIS CaliforniaFloridaTexas

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 CODIS INDICES

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. freq(A 1 ) = p 1 freq(A 2 ) = p 2 A 1 A 1 = p 1 2 A 1 A 2 = 2p 1 p 2 A 2 A 2 = p 2 2 p p 1 p 2 + p 2 2 = 1 Homozygous locus frequency = p 2 +p(1-p)  For homozygous loci, a Theta correction (  ) is used to account for population substructure

PART 2

XXX Obligate allele Dual Obligate alleles Paternity Exclusion

XXXX Obligate allele Paternity Exclusion

XX Obligate allele Dual Obligate alleles

Paternity Inclusion Obligate allele

Paternity Inclusion Obligate allele Dual Obligate alleles Dual Obligate alleles

Paternity Inclusion Obligate allele

Several Statistical Values are Calculated to Assess the Strength of the Genetic Evidence If the Alleged Father Cannot be Excluded Paternity Index Combined Paternity Index Probability of Paternity Probability of Exclusion PI CPI W PE

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 % 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