Question

Write explanatory notes on the following: (i) Transgenic plants (ii) Transfer of recombinant DNA into host cells.

Answer 1

Step 1: (i) Transgenic Plants — Definition:
Plants that carry and express a foreign gene, introduced into them using genetic engineering techniques, are called transgenic plants.

Step 2: (i) Transgenic Plants — Purpose and Example:
This foreign gene confers a desired trait, such as pest resistance in Bt cotton (which carries a cry gene from the bacterium Bacillus thuringiensis), herbicide tolerance, or improved nutrition, such as Golden Rice, which is enriched with beta-carotene.

Step 3: (ii) Transfer of Recombinant DNA — Making Cells Competent:
After a desired gene is inserted into a suitable vector to form recombinant DNA, it must be introduced into a host cell. Bacterial cells are made 'competent' to take up DNA by treating them with a specific concentration of a divalent cation, such as calcium chloride, which increases the efficiency of DNA entry through the pores in the cell wall.

Step 4: (ii) Transfer of Recombinant DNA — Introducing the DNA:
The recombinant DNA is then incubated with the competent cells on ice, followed by a brief heat shock at 42 degrees Celsius and then putting them back on ice, causing the bacterial cells to take up the recombinant DNA (transformation).

Step 5: (ii) Transfer of Recombinant DNA — Direct Methods:
Alternative direct methods are also used, especially for plant and animal cells: microinjection, in which recombinant DNA is directly injected into the nucleus of an animal cell; the gene gun/biolistic method, where high-velocity DNA-coated microparticles are bombarded into plant cells; and the use of a disarmed pathogen vector such as Agrobacterium tumefaciens, which naturally transfers DNA into host plant cells.

Final Answer:
\(\text{Transgenic plants (e.g. Bt cotton, Golden Rice) carry a foreign gene; recombinant DNA is delivered into host cells by making them competent (CaCl}_2\text{, heat shock) or by microinjection, gene gun, or Agrobacterium vectors}\)