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

2. 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

3. 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

4. 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

5. 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

6. What Is a DNA Fingerprint?

7. Preparing a DNA Fingerprint

8. Preparing a DNA Fingerprint

9. 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)

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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.

16. 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.

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