FORENSIC DNA TESTING

• There have been main types of forensic DNA testing. They are often called, RFLP and PCR based testing, although these terms are not very descriptive. Usually, RFLP testing requires larger amounts of DNA and the DNA must be undegraded. Crime-scene facts that is elderly or that is present in tiny amounts is often unsuitable for RFLP testing. Warm damp conditions may speed up DNA degradation rendering it unsuitable for RFLP in a comparatively short time period. 

• PCR-based testing often requires less DNA than RFLP testing and the DNA may be partially degraded, more so than is the case with RFLP. However, PCR still has sample size and degradation limitations that sometimes may be under-appreciated. PCR-based tests are also very sensitive to contaminating DNA at the crime scene and within the check laboratory. In the work of PCR, contaminants may be amplified up to a billion times their original concentration. Contamination can influence PCR results, without proper handling techniques and proper controls for contamination.

• PCR is less direct and more liable to error than RFLP. However, PCR has tended to replace RFLP in forensic testing primarily because PCR based tests are faster and more sensitive.