30.06.2014 Views

John M. S. Bartlett.pdf - Bio-Nica.info

John M. S. Bartlett.pdf - Bio-Nica.info

John M. S. Bartlett.pdf - Bio-Nica.info

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

260 Case-Green, Pritchard, and Southern<br />

Fig. 4. Synthesis of an array for typing F13 locus.<br />

methods have proved inadequate for choosing the oligonucleotide sequences because<br />

many factors, such as the position of mismatches and secondary structure in both<br />

the oligonucleotides and target, affect the duplex yield. An empirical solution to<br />

this problem is to test various conditions using combinatorially synthesized arrays<br />

containing many of the possible oligonucleotides complementary to the allele being<br />

investigated (13,14).<br />

1.4. Enzyme-Aided Assays<br />

1.4.1. SNPs<br />

Several variants of the hybridization/extension method are suitable for the analysis<br />

of (biallelic) SNPs (Fig. 5B,C) (15,16). In the simplest form, two oligonucleotides are<br />

synthesized that differ in their terminal base; the two bases complementary to the<br />

bases to be analyzed. Hybridization of the target sequence will occur in similar yields<br />

to both oligonucleotides because of the poor discrimination at terminal bases (17).<br />

Ligases and polymerases can distinguish the two duplexes and are able to extend<br />

only oligonucleotides with the matching base. Labeled nucleotide triphosphate,<br />

complementary to the first base after the allelic position in the target, is incorporated<br />

only on oligonucleotides, which form perfect duplex. The position of the label<br />

on the support indicates the sequence that is complementary to the target (Fig.<br />

5C). Alternatively, a common primer can be used and labeled nucleotide added<br />

complementary to either of the alleles of interest in the target. Only when the nucleotide<br />

added is complementary to the biallelic position will the primer be extended. (Fig.<br />

5B) Ligation can also be used in these assays, replacing the nucleotide triphosphates<br />

with labeled reporter oligonucleotides having terminal bases complementary to the<br />

alleles to be analyzed.<br />

1.4.2. STR Typing<br />

A method for measurement of STR length is shown in Fig. 3. As with SNP typing,<br />

assays using both DNA ligases and DNA polymerases are possible. In the basic ligation<br />

assay, the target sequence plus a reporter oligonucleotide complementary to the distal

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!