Though forensic DNA analysis is very powerful and reliable, this method is also subject to human error which could then result in incorrect convictions. The employment of forensic DNA analysis is very critical in cases wherein no other supporting evidence could be collected from the crime scene, the victim or the suspect. Errors in handling forensic DNA may include contamination, wherein the samples employed in the analysis contains a mixture of more than one biological organism, which may be either another individual different from the actual analyzed person, as well as DNA from bacteria that may be present at the site of collection.
Another error in handling forensic DNA samples may also involve degradation of the sample, which pertains to the breakage of the DNA in the samples collected (Coble and Butler, 2005). Intact DNA is necessary is performing STR analysis and degradation of DNA could result from exposure of the collected samples to heat or reagents such as acid, bleach, alcohol or preservatives such as formalin or acetone.
Heat associated to a crime scene may be due to a fire or burning of only a particular part of the crime scene where the collected sample was situated. Intact DNA is necessary for the success of an STR analysis because the STR sequences have to be located in the entire genome of an individual and any breakages in the genome would result in an erroneous result in the analysis, wherein either an STR region may not be identified because that particular region could not detected because it was probably located in the region that was degraded.
It should be understood that although forensic DNA analysis requires specific conditions for sample collection and DNA handling, the procedure is very reliable and robust that even samples that have been stored in preservative or alcohol for decades or centuries may be employed as source of DNA for STR analysis. In order to prevent contamination of samples that will be used for forensic analysis, quality-control procedures have been designed in order to have a standardized method of conducting any collection and handling of material.
The use of protective wear such as gloves, face masks and laboratory gowns are necessary in handing forensic samples. In addition, structural equipment such as HEPA-filtered air duct systems, biological hoods and clean rooms are also necessary to ensure that contamination does not occur during the analysis. The systematic labeling and recording of forensic samples and DNA material are also important in the success of DNA analysis.
It is actually better and simple for the forensic scientist to rule out any problems with contamination and just focus on analyzing any similarities in the DNA profiles of the individuals being investigated in the forensic laboratory. Aside from employing forensic DNA analysis in crime investigations, STR analysis may also be employed in the identification of victims in mass fatalities or disasters such as bombings, tsunamis, plane crashes and mass graveyards (Budimlija et al.
, 2003). In such conditions, wherein not only two individuals (victim and suspect) are involved, a more tedious process of collection, handling and analysis of DNA samples is conducted. Forensic DNA analysis of victims in a mass disaster needs references samples which actually pertain to material to will facilitate in the positive identification of a body. Two kinds of reference samples are generally employed in this type of forensic analysis.
The DNA samples collected from the victim’s family members are employed as a reference sample. Personal effects of a victim are also employed as reference samples such as biological specimens that may have been collected before death or antemortem, biopsies from the hospital in which the victim may have gone to for medical consultation, or bloodstain cards of the victim that may be been issued during a biomedical test.
Simple antemortem reference samples are also admissible for forensic analysis and these may include toothbrushes, razors and and shavers, yet these reference samples may generate errors in the analysis because these items may also be contaminated with DNA from other individuals or other biological organisms such as bacteria or fungi.