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Explain the proper collection and packaging methodologies for biological evidence. Why should biological evidence never be packaged in air-tight or non-breathable mediums?

When a crime is committed, there is usually evidence that is left behind. This evidence will point to the parties that were involved in the event as well determining what happened. Biological evidence is very credible but is also very fragile. Contamination as well as destruction of this evidence can happen very easily. To avoid this, there are particular methods for both collecting and packaging biological evidence. 

Biological evidence can be defined as any evidence that can contain DNA. This can include blood, saliva or other body fluids, hair, bones, fingernails or skin samples as well as objects containing either fluids or specimens. Evidence that is found in a liquid form should be collected using sterile swabs. After collecting them, they should be labeled and left to dry in a cool place away from direct sunlight as well and wind so that contamination does not occur. Once they have dried, they should be labeled and packaged in paper envelopes. Dried evidence such as blood can be collected by sending the entire object to the lab, or if that is not possible due to the object size or location, the evidence can be scraped off into paper, then sealed in an envelope, labeled and sent off to the lab (Schiro, n.d.) or sterile swabs can be moistened with sterile distilled water and used to rehydrate the sample for collection, then allowed to dry before packaging in paper envelopes (Warrington, 2009). Fluid that is found pooled is best collect by using a 1”x1” piece of cotton muslin and absorbing the stain, letting it dry, then packaging for the lab (Schiro, n.d.).  Hair, nail and bone samples should be collected in separate paper envelopes and labeled. Clothing or bedding should be allowed to dry so no transfer staining occurs, then carefully folded and placed in a paper bag for processing (Bevel & Gardner, 2008).  Any objects that are found that have the biological evidence on them should be allowed to dry, then placed in paper envelopes or cardboard box depending on the size (Schiro, n.d.).

 Biological evidence should never be collected and stored in plastic packaging. This evidence by nature contains moisture and enclosing it in a nonbreathable package will encourage the growth of mold which will destroy the evidence. Biological evidence must be allowed to dry completely before being packaged (Schiro, n.d.). The buildup of moisture that is generated from the evidence can cause a humid environment and even if mold does not begin to grow, it can still further deteriorate the evidence. 

What is PCR analysis? Why is this application important particularly for cold cases or cases in which only a small amount of DNA is recovered? 

Polymerase chain reaction or PCR, is a method that allows for the multiplication of DNA for the purpose of analyzing. The PCR process relies on an original DNA base, primers, nucleotides and a DNA polymerase to create additional DNA. PCR is excellent for use in cold cases because there only needs to be a very tiny amount of DNA obtained in order to duplicate it. This DNA can also come from any source such as body tissue, hair, blood, saliva, or any other DNA containing specimen (Garibyan & Avashia, 2013).  

What is STR analysis? Why is this an effective method for DNA typing?

Short tandem repeat or STR is similar to fingerprint analysis and identification. STR uses specific regions in the nuclear DNA for comparison and identification. The variations of these areas or individual characteristics is what distinguishes one DNA profile from another and creates an identification. This method of DNA typing is effective because outside of identical twins, the probability of two people having the same DNA profile is 1:1 billion (NIJ, 2012). 


Bevel, T. & Gardner, R. (2008). Bloodstain Pattern Analysis: With an Introduction to Crime Scene Reconstruction. Retrieved from

Garibyan, L., & Avashia, N. (2013). Polymerase chain reaction. The Journal of investigative dermatology, 133(3), 1–4. doi:10.1038/jid.2013.1

National Institute of Justice. (2012). DNA Evidence: Basics of Analyzing. Retrieved from

Schiro, G. (n.d.). Collection and Preservation of Blood Evidence from Crime Scenes. Retrieved from

Warrington, D. (2009). DNA Collection and Packaging. Retrieved from

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