# Presentation: 260418

## Brief History of Forensic DNA Typing

- 1980 - Ray White describes first polymorphic RFLP marker
- 1985 - Alec Jeffreys discovers multilocus VNTR probes
- 1985 - first paper on PCR
- 1988 - FBI starts DNA casework
- 1991 - first STR paper
- 1995 - FSS starts UK DNA database
- 1998 - FBI launches CODIS database

## DNA Use in Forensic Cases

- Most are rape cases (>2 out of 3)
- Looking for match between evidence and suspect
- Must compare victim’s DNA profile

- Mixtures must be resolved
- DNA is often degraded
- Inhibitors to PCR are often present

_**Challenges**_

## Human Identity Testing

- Forensic cases -- **matching suspect with evidence**
- Paternity testing -- **identifying father**
- Historical investigations
- Missing persons investigations
- Mass disasters -- **putting pieces back together**
- Military DNA “dog tag”
- Convicted felon DNA databases

## Steps in DNA Sample Processing

- _Biology_

- _Technology_

- _Genetics_

**Steps in DNA Sample Processing**

## Sources of Biological Evidence

**Blood**
**Semen**
**Saliva**
**Urine**
**Hair**
**Teeth**
**Bone**
**Tissue**

## DNA in the Cell

**DNA in the Cell**

## DNA Amplification with the Polymerase Chain Reaction (PCR)

**DNA Amplification with the Polymerase Chain Reaction (PCR)**

## PCR Copies DNA Exponentially through Multiple Thermal Cycles

**PCR Copies DNA Exponentially through Multiple Thermal Cycles**

## Short Tandem Repeats (STRs)

***the repeat region is variable between samples while the flanking regions where PCR primers bind are constant***

- 7 repeats

- 8 repeats

- Homozygote = both alleles are the same length
- Heterozygote = alleles differ and can be resolved from one another

## TCAT repeat unit

*Different primer sets produce different PCR product sizes for the same STR allele*

## Over 10 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

- Over 10 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

## An Example Forensic STR Multiplex Kit

## Available Kits for STR Analysis

- Kits make it easy for labs to just add DNA samples to a pre-made mix
- 13 CODIS core loci
- Profiler Plus and COfiler (PE Applied Biosystems)
- PowerPlex 1.1 and 2.1 (Promega Corporation)
- Increased power of discrimination
- CTT (1994): 1 in 410
- SGM PlusTM (1999): 1 in 3 trillion
- PowerPlex TM 16 (2000): 1 in 2 x 1017

## ABI Prism 310 Genetic Analyzer

## Close-up of ABI Prism 310 Sample Loading Area

**Close-up of ABI Prism 310 Sample Loading Area**

***See Technology section for more information on CE***

## Slide 16

## STR genotyping is performed by comparison of sample data to allelic ladders

**STR genotyping is performed by comparison of sample data to allelic ladders**

## STR Allele Frequencies

- TH01 Marker

- **Proc. Int. Sym. Hum. ID (Promega)* 1997, p. 34

## FBI’s CODIS DNA Database

_**Co**_mbined _**D**_NA _**I**_ndex _**S**_ystem
- Used for linking serial crimes and unsolved cases with repeat offenders
- Launched October 1998
- Links all 50 states
- Requires >4 RFLP markers
-     and/or 13 core STR markers
- Current backlog of >600,000 samples

## 13 CODIS Core STR Loci with Chromosomal Positions

**13 CODIS Core STR Loci with Chromosomal Positions**

**CSF1PO**

**D5S818**

**D21S11**

**TH01**

**TPOX**

**D13S317**

**D7S820**

**D16S539**

**D18S51**

**D8S1179**

**D3S1358**

**FGA**

**VWA**

**AMEL**

**AMEL**