Biotechnology and Applied Botany
Tools and applications
The exam tests recombinant DNA tools, restriction enzymes, vectors, PCR, gel electrophoresis, plant transformation, tissue culture and applied products such as Bt cotton.
Core rules
- Restriction endonucleases cut DNA at specific sequences, often producing sticky ends; DNA ligase joins fragments.
- Plasmids such as pBR322 and the Ti plasmid of Agrobacterium are common vectors; they need an origin of replication, selectable marker and cloning site.
- PCR has denaturation, annealing and extension steps and uses Taq polymerase.
- Gel electrophoresis separates DNA by size; DNA is negatively charged and moves towards the anode.
- Plant tissue culture uses an explant, nutrient medium and auxin-cytokinin balance to induce callus and then shoots or roots.
- Micropropagation produces clones; somaclonal variation can be a source of new traits.
- Bt cotton carries a toxin gene from Bacillus thuringiensis; Agrobacterium-mediated transformation is widely used.
Worked example
A gene is inserted into the T-DNA of a Ti plasmid. Reasoning: Agrobacterium infects plant tissue and transfers T-DNA into plant cells; the gene is integrated into the plant genome. Transformants are selected using the marker carried by the vector, then regenerated by tissue culture.
Traps
PCR amplifies DNA; it does not cut it. Restriction enzymes cut; ligase joins. The Ti plasmid is a natural vector from Agrobacterium, not a plant gene. Callus formation is dedifferentiation, not direct seed germination.