Unlocking Genetic Codes: The Power of DNA Fingerprinting in Forensic Science

1. Chapter 11-DNA Profiling (or DNA Fingerprinting) & Forensics History Uses of DNA Profiling Hypervariable DNA sequences examined (RFLPs, VNTRs, STRs, SNPs, mitochondrial DNA, Y chromosomal DNA) Methods (Southerns & PCR) Statistical considerations Technical considerations Databases and Privacy

2. DNA Fingerprinting • You're 99.9% identical • But of course, you are unique--in a genome of three billion letters, even a 0.1 % difference translates into three million differences. • These differences (or polymorphisms) reside in several places in the genome, often in microsatellites • Examples of such polymorphisms include VNTRs, STRs, RFLPs and SNPs

3. DNA Fingerprinting • Focuses on the 0.1-1.0% of human DNA that is unique • First described in 1985 by Dr. Alec Jeffreys in England • DNA evidence is admissible in courts • Labs such as Cellmark Diagnostics and Lifecodes Corporation are examples of companies which provide such DNA evidence to courts, but states and many U.S. cities have labs for DNA fingerprinting • Have any of you worked in a crime lab?

4. Uses of DNA fingerprinting • Paternity testing • Identification of criminals (e.g. murderers, rapists, letter bombers) • Immigration disputes (family relationships) • Identification of deceased individuals with mutilated or decomposed bodies (e.g., the military, 9/11 victims) • Identifying the sperm donor who “decorated” Monica Lewinsky’s blue dress

5. How is DNA fingerprinting done? • DNA obtained from hair, semen, blood, sweat, saliva, bone or any other tissue (often found at a crime scene) • Can be done by southern blotting with an appropriate probe or by a PCR method using appropriate primers • Can use single locus probes/primers or multilocus probes/primers • DNA can be resolved on a gel or by a capillary electrophoresis system

6. Sequences examined in DNA fingerprinting • VNTRs-variable number tandem repeats; composed of 8-80 bp repeat units (e.g., [GCGCAATG]n) which are tandemly repeated so that the overall length is 1-30 kb • STRs-short tandem repeats; composed of 2-7 bp repeat units (e.g., [AC]n) which are tandemly repeated so that the overall length is less than 1 kb • RFLPs-restriction fragment length polymorphisms • SNPs-single nucleotide polymorphisms • Mitochondrial DNA-maternal inheritance, tends to be more stable than nuclear DNA • Y chromosome DNA- passed from father to son

7. DNA fingerprinting: an example • D1S80, a VNTR located on human chromosome 1, contains a 16 bp repeat unit • The number of repeats varies from one individual to the next, and is known to range from 14-41

8. Some examples of DNA fingerprinting • Paternity cases • Crime scenes

11. Determining the probability of a match • Relies on statistics • Analysis depends upon your ethic background (i.e. African American, Caucasian, Hispanic Asian, etc.)

13. Technical Considerations • Preserve the integrity of DNA sample • Avoid DNA contamination & degradation • Avoid incomplete digestions if REs are used • Use standard hybridization conditions • Use standard PCR primers and procedures • Gel analysis is less reproducible than capillary electrophoresis of PCR products • Difficulties in interpreting bands on a gel or X-ray film

14. DNA databases • Already in place in the FBI for convicted felons (i.e., CODIS-COmbined DNA Index System, involves 13 STR loci) and the Dept. of Defense for armed service personnel and the Virginia saliva and blood bank of convicted felons • A national DNA database has been suggested. What do you think? • Could current or potential employers or insurance companies base decisions they make on this kind of data?