DNA Fingerprinting

Mark Bailey

Vicki L. Burnett

Walker B. Carroll

What is it?

• Series of techniques used to differentiate one subject’s DNA from another

• Compares hypervariable regions, or variable numbers of tandem repeats (VNTRs)

• Synonyms are DNA profiling, DNA typing, DNA fingerprinting

Who developed it, and when?• Sir Alec Jeffreys, University of Leicester, England

in 1985• Identified hypervariable regions in the DNA• Published two key papers describing how those regions

could be used as ‘fingerprints’ for differentiating individuals, and how those fingerprints might be used in the criminal justice system

• First used in England in an immigration case, then to exonerate a suspect in a murder case

Jeffreys AJ, Wilson V, Thein SL (1985) Individual-specific ‘fingerprints’ of human DNA. Nature 316(4):76-79.Gill P, Jeffreys AJ, Werrett DJ (1985) Forensic application of DNA ‘fingerprints’. Nature 318(6046):577-579.

Technical advances

• Structure of DNA -Watson, Crick, Franklin

• Sequencing of DNA -Sanger

• Amplification of DNA by the polymerase chain reaction (PCR) -Mullis

• Restriction endonucleases to cleave DNA

• Gel electrophoresis to separate DNA

• Dyes or probes to visualize the DNA

What is it used for?

What is it used for?

• Paternity cases, babies in maternity ward• Forensic science to identity remains of dead

bodies as well as live folks• Characterization of genomes, cell lines,

plant lines• Trace transmission of diseases such as TB

and food-borne pathogens• Identify genetic mutations in cancer, other

diseases• Identify lineage of populations

Advantages

• Probability of two people having the same fingerprint is very small

• DNA profile can’t be altered by suspect• DNA remains intact under many harsh

conditions• May be able to obtain information about an

individual from a relative’s DNA• Leads as much to exonerations of wrongly

accused suspects as convictions of guilty ones

Disadvantages

• Fingerprint is a very small part of the genome, uniqueness questioned

• Matches within certain ethnic groups may be much higher than in other populations

• Human error either at the crime scene, the laboratory, or the police station

• Ethical issues pertaining to identification of genetic defects or medical conditions

DNA data banks• All 50 states have rules on collection of

DNA profiles from criminal cases

• National Combined Data Index System in place (CODIS) in searchable database

• Battery of 13 different markers used

• International databanks incorporating similar markers to facilitate identification of criminals across countries

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