PCR (Polymerase Chain Reaction)
Definition
A method for amplifying specific DNA sequences from very small or degraded samples, developed by Kary Mullis in 1983. PCR made DNA profiling feasible from trace evidence, including single hairs, touch DNA, and aged bloodstains. It forms the basis of all modern forensic STR and other profiling methods.
- Developer
- Kary Mullis, 1983
- Impact
- Made DNA profiling feasible from trace evidence
- Applicable to
- Single hairs, touch DNA, aged bloodstains
- Role today
- Basis of all modern forensic STR and other profiling methods
Common questions
Why couldn't forensic labs profile trace DNA samples before PCR existed?+
Earlier DNA typing methods such as RFLP required a comparatively large, intact quantity of DNA to produce a readable result, which most trace samples like a single hair root or a small touch deposit simply did not contain, making them untestable before amplification technology existed.
Does PCR amplify contaminant DNA as readily as the DNA of interest?+
Yes, PCR amplifies whatever target-compatible DNA is present in the reaction, including trace contamination, which is why strict anti-contamination protocols in evidence handling and the lab are essential to avoid amplifying and reporting DNA that did not come from the item examined.
Related terms
- ABO Blood Group System
- Classification of red blood cells by the presence or absence of A and B antigens on the cell membrane, determined by alleles...
- Mitochondrial DNA (mtDNA)
- DNA located in mitochondria rather than the cell nucleus. Present in hundreds to thousands of copies per cell, making it recoverable from...
- RFLP (Restriction Fragment Length Polymorphism)
- The first DNA profiling method used in forensic casework, developed by Alec Jeffreys in 1984. Restriction enzymes cut DNA at specific sequences,...
- STR (Short Tandem Repeat)
- A genomic locus where a 2, 7 base-pair unit is repeated in tandem a variable number of times between individuals. The variation...
- Touch DNA
- Minute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points...