Examination of Firearms Review: 2007 to 2010 - Interpol

lood; HTN3 and STATH for saliva; PRM1 and PRM2 for semen; MUC4 for vaginal
fluid; and S15 as housekeeping gene. Samples that were exposed to the natural
outside environment exhibited dramatically reduced recovery compared to room
temperature and light exposed samples. UV- and luminescent light did not have an
impact on the recovery values of RNA from blood and saliva samples. Semen
samples exhibited increased RNA recovery. It is speculated that the light treatment
enhances RNA isolation from spermatozoa by facilitating the disruption of cellular
integrity. Vaginal samples however exhibited a significant reduction in RNA recovery
upon treatment with UV, but not luminescent light. This might be caused by
germicidal actions, as a vaginal swab is expected to contain microbial communities
from the female reproductive tract. More research can be expected, unravelling the
molecular basis of mRNA degradation, including whether the 5’ end, the 3’ poly-Atail,
or the intervening sequences are specifically degraded or whether nucleolytic
damage is randomly distributed.
3.5.2 MicroRNA
As discussed above, RNA degradation is promoted by environmental factors (e.g. UV
light, moisture, and heat) 15 . This degradation will negatively affect the detection of
RNA. To reduce this negative effect, miRNAs can be used instead of mRNA,
because of their shorter amplicon length 16 . Zubakov et al 15 , published that blood and
semen samples aged for 1 year under lab conditions (relatively constant humidity
and ambient temperature, no UV exposure, dust free, etc.) still contained a
detectable amount of miRNAs. It seemed that the aging had no negative effect on the
absolute level of miRNAs that could be detected. Furthermore the effect of
environmental factors on miRNA still needs to be investigated. Although it can be
expected that miRNA degradation is influenced by the same environmental factors as
mRNA.
4. Evidence individualization
4.1 Introduction
After samples are collected and have shown to be of value for further examination
(by e.g. identity testing) the individualization process begins. Individualization is used
to prove with a certain amount of confidence that the evidence originates from the
suspect or another individual, thereby linking the biological trace evidence to its
donor.
4.2 DNA typing
Base sequence variations in the human genome can be used for DNA typing, which
is also known as DNA identification analysis, identity testing, DNA testing, genetic
fingerprinting, genotyping, or DNA profiling. DNA as a tool for the individualization of
biological samples was introduced by Sir Alec Jeffreys in 1985 22 . Every human
(except identical twins), each possesses a unique genotype, furthermore the DNA of
an individual is identical whether it is extracted from buccal cells, white blood cells, or
spermatozoa (note that each spermatozoa contain only half of the DNA due to
meiosis). These principles of individual uniqueness and identical DNA structure within
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