Geoscience Reference
In-Depth Information
more advanced with a wide range of thermostable DNA poly-
merases (such as
Taq
,
Pfu
and
Vent
polymerase) and automa-
tion of reactions can be done by a thermocycler, which has
found its way into nearly every molecular biology lab in the
world. The major advantages of PCR techniques compared to
hybridisation-based methods include (Semagn et al. 2006):
1. A small amount of DNA is required.
2. Elimination of radio-isotopes in most techniques which
are health hazardous.
3. The ability to amplify DNA sequences from preserved
tissues.
4. Accessibility of methodology for small labs in terms of
equipment, facilities and cost.
5. No prior sequence knowledge is required for molecular
markers like AP-PCR, RAPD, DAF, AFLP and ISSR.
6. High polymorphism that enables generating many genetic
markers within a short time.
7. The ability to screen many genes simultaneously either
for direct collection of data or as a feasibility study prior
to nucleotide sequencing efforts (Wolfe and Liston 1998).
These advantages, however, can vary depending on the
specific technique chosen by the researcher. The PCR-based
techniques can be categorised into two types, depending on the
primers used for amplification:
1. Arbitrary or semi-arbitrary primed PCR techniques that
are developed without prior sequence information (e.g.
AP-PCR, DAF, RAPD, AFLP, ISSR).
2. Site-targeted PCR techniques that are developed from
known DNA sequences (e.g. EST, CAPS, SSR, SCAR,
STS).
17. 4
Section II: Molecular markers for crop
improvement
The rising global population will require increased crop pro-
duction and productivity with sustainable agriculture. This
required increase in crop production needs to occur in the
context of mounting water scarcity, decreasing area and envi-
ronmental degradation of arable land, increasing pollution and
possible adverse effects of climate change. Thus, the task of
increasing crop yields represents an extraordinary challenge
