Biology Reference
In-Depth Information
A
T
(a)
5
′
-TGCATCGTCACGTGACTGCTAGTCAAT - 3
′
Template
T
GCACTGACGATCAGTTA - 5
′
Primer
(b)
(c)
Figure 12.4
The primer extension assay. (a) The target sequence is amplified using PCR and the
products are used as the template in the extension assay; (b) an internal primer hybridizes to the
target adjacent to the SNP and a single fluorescently labelled ddNTP is added by
Taq
polymerase;
(c) the labelled single-base extension (SBE) product is analysed using capillary electrophoresis
ASO probe
T
ASO probe
T
A
Target
G
Target
(a)
(b)
Figure 12.5
Allele-specific hybridization: allele-specific oligonucleotide (ASO) probes that include
the SNP are hybridized with the target DNA. (a) Under highly stringent conditions only perfectly
matched sequences will form stable interactions and (b) with one mismatch in sequence the ASO
will not hybridize
Forensic applications of SNPs
A vast amount of data is available on the different SNPs in the human genome and
one of the biggest tasks when applying SNPs to forensic applications is to select
the most appropriate SNPs from the overwhelming numbers that are available. The
choice of SNPs is very much dependent on the application. The characteristics that
a SNP must fulfil are that they need to be polymorphic, that is with not one allele
