Page 42 - 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

DNA Testing in Forensic Science 593

FIGURE 2 A generalized eukaryotic cell showing the organization and distribution of organelles as they would appear
in transmission electron microscope. The type, number, and distribution of organelles are related to cell function. (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.)

between 0 (carpet stains or putrefied samples) and 61.5% 15-min increments, up to 1 hr are presented in Fig. 3. There
(scrapped dried stains) of the time with and average of is a linear decrease in high-molecular-weight DNA with
52% for the 100 items of evidence tested.. Thus, the ma- the UV germicidal light, such that after an hour about 96%
terial DNA is deposited on and the degree of further in- of the high-molecular-weight DNA has been lost. Even in
sult can markedly affect the ability to obtain RFLP DNA the weak midday light in January, over 60% of the high-
results. molecular-weight DNA was lost. In contrast, the fluores-
All of the published studies on environmental insult cent lighting in the laboratory and the after sunset light had
were done on prepared dried stains. Since biological flu-
ids are liquid the effects of ultraviolet radiation on liquid
DNA have been evaluated. The results of exposing 100-µl
samples of a standard DNA solution to fluorescent light
in the laboratory, a UV germicidal light (254 nm), mid-
day sunlight in January, and early sunset light in January in

TABLE I DNA Content of Various Tissues
1 sperm 3 pg
1 cell 6 pg
1 shed hair 1 ng a
1 plucked hair 300 ng b
1 drop of blood 1,500 ng
a
The success rate for PCR on shed hairs is 30 to 50%, FIGURE 3 Plot of DNA concentration (frorescence) over time
so this average is optimistic. after exposure to different light sources. (From Schanfield, M. S.
b There is a great deal of variation among hair roots. (2000). Deoxyribonucleic Acid/Basic Principles. In “Encyclopedia
Fine blond hair will tend to have much less DNA, while of Forensic Sciences” (Siegel, J. A., Saukko, P. J., and Knupfer,
course dark hair with large roots more. G. C., eds.), Academic Press, London, p. 482.)