Biology Reference
In-Depth Information
being very common and the other very rare, and that they can be examined at the
same in a multiplex similar to that for STR loci.
Forensic identification
The vast majority of forensic DNA analysis involves the characterization of biological
material recovered from the scene of a crime. Several panels of SNPs have been
developed that are designed to provide maximum discrimination powers for forensic
identification [29, 42, 43]. These contain SNPs that are polymorphic in all major
population groups. A panel containing 52 SNPs was developed by the SNPforID
Consortium [29]. Using this panel of SNPs produced match probabilities that ranged
from 5.0
×
10
−
19
in an Asian population to 5.0
×
10
−
21
in a European population.
When applied to paternity testing, average paternity indices of between 336 000 in
Asian populations and 550 000 in European populations were achieved.
However, even with the high discrimination power, the effort involved in
analysing 50 SNPs is greater than when undertaking standard STR analysis. The
major attractions of using SNPs with the current technology is that SNP analysis can
provide results from highly degraded DNA when conventional STR profiling has
failed [42, 44] and also the low mutation rate of SNPs.
Prediction of the geographical ancestry
In many cases, the identification of the population group from which a crime scene
sample has come from can be valuable intelligence for the investigating agencies:
was the person who left the material at the crime scene of Caucasian, Asian, African,
mixed ancestry? Panels consisting of mtDNA SNPs and Y SNPs have already been
found useful for this purpose [45, 46] but are intrinsically limited by the fact that they
can only provide information on either the maternal or paternal ancestry. Autosomal
SNPs that have different frequencies in different major population groups can provide
valuable information on geographic ancestry [47, 48]. Many of the SNPs selected for
this purpose are associated with coding regions that have been subjected to selection
pressures. These include pigmentation genes and genes involved with the metabolism
of xenobiotics. The pigmentation genes, in addition to providing information on
geographic ancestry, can also give information on phenotype of the person who
deposited the biological material at a crime scene, including skin, hair and eye
colour [49 - 52].
SNPs compared with STR loci
Current STR-based multiplex kits like AmpF
STR
Identifiler
and PowerPlex
16
can amplify 15 STR loci and the amelogenin locus. Using the current technology it is
difficult to co-amplify and detect any more STR loci. Also, the size of the amplicon
for each STR is quite large. The great advantage STRs have over SNPs is their power
