Biology Reference
In-Depth Information
An essential feature of any STR used in forensic analysis is that biological material
should give an identical profile regardless of the individual or laboratory that carries
out the analysis. Without this standardization it would not be possible to compare
results between laboratories, and developments such as national DNA databases
would not be possible [7 - 11]. All new multiplexes have to be vigorously validated
before they are used for the analysis of casework [12 - 20].
The UK Forensic Science Service (FSS) developed the first STR-based typing sys-
tem that was designed for forensic analysis in 1994. Four STR loci were amplified in
the same reaction [16, 21, 22]. This was replaced by the second generation multiplex
(SGM), which was also developed by the FSS [23 - 25]. With the increased adop-
tion of STR multiplexes worldwide, two commercial companies, Applied Biosystems
and Promega Corporation, have developed a series of multiplexes that are now used
by most laboratories. The AmpF
STR
SGM Plus, which is produced by Applied
Biosystems replaced the SGM in the UK and has been adopted by many other coun-
tries around the world as one of their standard multiplex kits [12]. In the USA, STR
technology was adopted into forensic casework following a survey of 17 previously
characterized STR loci, and in 1997 13 loci were selected as the Combined DNA
Index System (CODIS) loci [8, 26]. These loci can be analysed in one PCR using
one of two commercially available kits; the AmpF
STR
Identifiler
produced
by Applied Biosystems [27] and the PowerPlex
16 produced by Promega Cor-
poration [14]. Additional commercial kits are available that incorporate additional
loci, for example the SinoFiler
, which has been designed for the Chinese market,
and replaces four of the loci found in the Identifiler
[28]. The STR loci that are
incorporated into some commonly used multiplexes are shown in Table 6.1.
In addition to STR loci, the amelogenin locus, which is present on the X and Y,
chromosomes has been incorporated into all commonly used STR multiplex kits. The
amelogenin gene encodes for a protein that is a major component of tooth enamel
matrix; there are two versions of the gene, the copy on the X chromosome has a
6 bp deletion, and this length polymorphism allows the versions of the gene on the
X and Y chromosomes to be differentiated [29] (Figure 6.2).
Y chromosome
6 bp deletion
X chromosome
Figure 6.2
The amelogenin locus is present on both the X and Y chromosomes. The gene that is
present on the X chromosome has a 6 bp deletion. The primers (schematically shown by the arrowed
lines) that were reported by Sullivan
et al
. [29] led to products of 106 bp from the X chromosome
and 112 bp from the Y chromosome
