Page 41 - Academic Press Encyclopedia of Physical Science and Technology 3rd Molecular Biology

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Encyclopedia of Physical Science and Technology EN004L-956 June 9, 2001 21:7

592 DNA Testing in Forensic Science

FIGURE 1 Molecular structure of DNA. From top to bottom: Adenine–Thymine, Guanine–Cytosine, Adenine–
Thymine and Guanine–Cytosine. (From Schanfield, M. S. (2000). Deoxyribonucleic Acid/Basic Principles. In
“Encyclopedia of Forensic Sciences” (Siegel, J. A., Saukko, P. J., and Knupfer, G. C., eds.), Academic Press, London,
p. 481.)

successfully obtained from blood and bloodstains, vagi- PCR based tests are set up to use between 1 and 10 ng of
nal and anal swabs, oral swabs, well-worn clothing, bone, genomic DNA.
teeth, most organs, and to some extent urine. It is less likely
to obtain DNA from some types of evidence than others.
C. Destruction of DNA
Blood or semen stains on soil and leather are historically
not good sources of evidenciary DNA. Saliva, per se, has Biological materials are going to be affected by their en-
few nucleated cells, but, beer and wine bottles, drinking vironment. Enzymes lose activity over time and type of
glasses, beer cans, soda cans, cigarettes, stamps and enve- storage conditions. DNA has been found to be relatively
lope flaps have all been found to provide varying amounts robust when it is in the form of dry stains. Initial envi-
of DNA. ronmental studies indicated some of the limitations of
DNA based on the material it is deposited upon and the
environmental conditions. Environmental insult to DNA
B. How Much DNA Is Needed
does not change the results of testing, you will either ob-
for Forensic Testing?
tain results, or if the DNA has been too badly affected
The amount of DNA needed to perform testing depends by the environment (i.e., the DNA is degraded) you do
on the technology used. RFLP technology usually needs at not get RFLP results. One report on the success rate of
least 50 ng of intact high-molecular-weight DNA. In con- obtaining RFLP results and noted that depending on the
trast PCR-based testing can use as little as 250 pg. Most substrate or condition of the stain, results were obtained