Examination of Firearms Review: 2007 to 2010 - Interpol

all tissues of the same body provide the basis for DNA profiling 23 . DNA typing has
completely pushed away conventional genetic typing methods such as blood group
typing and analysis of polymorphic enzymes. Forensic DNA typing can be used to
identify a suspect and to show someone's innocence. DNA typing methods can also
be used to prove kinship in civil cases and for the identification of individuals after a
mass disaster (flight accidents).
4.3 Epigenetics
Besides variations in the genotype, there are the so called epigenetic variations.
Epigenetics is to some degree responsible for phenotypic alterations 24 . Most
phenotypic alterations are caused by the genetics of an individual, but how does
epigenetics work when we know that the base sequence of the DNA is not altered?
The expression of certain genes may be increased by or inhibited through
biochemical modifications of the DNA and histones 25 , the proteins around which the
DNA coils that are crucial for DNA compacting into chromatin. Neither the gene
structure nor the nucleotide sequence is modified. The process of biochemical DNA
modification involves methylation of DNA molecules in many sites and acetylation,
phosphorylation, methylation and ubiquitination of histones 24 . Such epigenetic
modifications, so-called epigenetic markers, appear progressively throughout an
individual’s life and with increasing frequency as the individual ages. They are the
unexpected explanation to the phenotypic variations observed during aging. They
probably also explain some of the phenotypic differences observed among
monozygotic twins. A case study by Bach 24 revealed that about one third of identical
twin pairs show differences in DNA methylation patterns. Furthermore nothing
indicates today that epigenetic markers are transmitted beyond a limited number of
generations.
4.4 Short Tandem Repeats
Of all the DNA in a cell approximately 2% is coding for heritable traits, while the other
98% is ‘non coding’ 26 . Genetic mapping and sequencing studies have led to the
discovery of highly variable regions 27 in the non-coding part of DNA between different
individuals. These hypervariable regions, often termed minisatellites 22 and
microsatellites (or short tandem repeats - STRs), are generically known as VNTRs
(Variable Number Tandem Repeats) and are found at many sites throughout the
genome. Each VNTR contains a defined sequence of nucleotides which is repeated
a number of times in a tandem fashion, for example TCAT TCAT TCAT TCAT, the
greater the number of repeats, the longer the VNTR. The number of tandem repeats
in any particular minisatellite or microsatellite varies from one person to another. This
is exploited in identifying individuals on the basis of their DNA profile. The size of the
fragments identified will depend on the number of repeats that each microsatellite
contains, and the pattern (a series of peaks 28 ) obtained after capillary electrophoresis
(CE) is characteristic of the profiled individual 29 , except for identical twins, although
they might be distinguished when examining epigenetic markers 24 .
Fourney, DesRoches and Buckle 1 discussed the developments in STR technology
until 2007 and mentioned the usage of Y-STRs when examining genetic genealogy.
In the following three years new developments occurred and some will be discussed
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