1. DNA Fingerprinting
DNA Profiling

2. Purposes: Determine Identity (match tissue samples)
Establish Paternity

3. DNA as Forensic Evidence
Individual evidence – identify a single person
Trace evidence – small amount left at crime scene
Found in saliva, blood, semen, skin, hair roots, urine (nuclear DNA)
Hair, bones, teeth (mtDNA)

4. Collection of DNA Avoid contamination Preserve carefully
Wear gloves, avoid sneezing or coughing
Preserve carefully
Air-dry samples
If wet, store in freezer

5. Basic DNA Facts: Stores genetic information
Tightly coiled to form chromosomes
deoxyribonucleic acid
4 nitrogen bases: A (adenine), G (guanine), C (cytosine), T (thymine)
Double-stranded
Structure discovered by Watson and Crick

6. Basic DNA Facts: Found in nucleus of cells
Approx. 3 billion base pairs
Exons: encoded DNA
<1.5% of DNA
Introns: uncoded DNA (“junk” DNA?)
> 98.5% of DNA
Mitochondrial DNA (mtDNA): inherited only from mother
Only identical twins have identical DNA

7. Chromosomes Each person has 46 chromosomes
23 pairs – 1 set from mom, 1 set from dad
Genes: segment of DNA that contains info to produce a protein
Allele: alternate forms of a gene
Inherit 1 allele from mom, 1 allele from dad

8. Examine an individual’s DNA sequence to develop a DNA fingerprint
DNA Profiling:
Examine an individual’s DNA sequence to develop a DNA fingerprint

9. Steps of DNA Fingerprinting
Extraction: take DNA out of cells
Amplification: make copies of DNA
Use PCR (polymerase chain reaction)
Electrophoresis: DNA pieces separated within an agarose gel or capillary tube
Visible bands of DNA form a unique pattern
Pattern = “fingerprint”

10. PCR Machine: Amplifies (makes copies of) DNA

11. Gel Electrophoresis

12. DNA Fingerprint (using gel electrophoresis)

13. DNA TESTING 99.9% of DNA shared by humans
Polymorphisms: differences in DNA sequences (0.1%)
RFLP Analysis – older method, requires quarter-sized DNA samples
STR (short tandem repeat)
Within noncoding DNA regions (loci), 2-5 bases in length repeated
Very small or degraded DNA samples
Examine 13 regions (loci) for forensic analysis
Most current technology in use!

16. Capillary Electrophoresis (CE)

17. DNA Profile

18. Crime Scene Matching (To establish identity – all bands must match)

19. Paternity A child inherits 1 set of genes from mom, 1 set from dad
½ of the bands in a pattern are from mom; the other ½ from dad

20. Lab 15: Who did it?

21. Lab 15: Who did it?

22. Lab 15: Who did it?

23. mtDNA – trace maternal relatives
Evidence: hair, old bones/teeth
Famous case: Anna Anderson = Anastasia Romanov (Russian princess)? No
Y-STR – trace paternal relatives
Y-chromosome analysis
Famous case: Did Thomas Jefferson father children with his slave, Sally Hemmings?
Blood taken from descendents of Jefferson’s uncle & Hemming’s sons
Yes

24. CODIS Combined DNA Index System Electronic database of DNA profiles
Fully operational since 1998
Profile = 13 loci from STR analysis
1 in a Quadrillion possibility of a match
As of February 2011:
9.4 million offender profiles (DNA from convicted felons of violent crimes)
360,000 forensic profiles (DNA from crime scenes)
138,700 hits made

25. CODIS (continued) STR Profiles entered into CODIS: Convicted offender
Forensic (crime scene DNA)
Arrestees
Unidentified human remains
Biological relatives of missing persons
Future of CODIS:
mtDNA (degraded samples, hair, bones, teeth)
Y-STR (sexual assault)
miniSTR (highly degraded samples)

26. Uses of DNA in Forensic Identification
Identifying September 11th victims
DNA Shoah Project: genetic database of people who lost family during the Holocaust
Disappeared children in Argentina (1970’s)
Tomb of the Unknowns (Arlington National Cemetery)
Remains of Romanov family (last Russian Czar)
Evolution of human migration patterns