Briefly describe the modes of DNA transfer into the host.
Transfer of foreign DNA into a host cell is one of the basic steps in rDNA technology. In nature, bacteria obtain foreign DNA from their surroundings through three ways: transformation, transduction, and conjugation.
Transformation is the genetic alteration of a cell resulting from direct uptake of exogenous DNA from surroundings through the cell membrane, which gets incorporated into the recipient genetic material. Recipient cells with foreign DNA are called transformants.
Transduction involves viruses mediating the uptake of foreign DNA into the genome. Bacteriophages infect bacteria and in the lysogenic cycle, their genome gets incorporated into bacterial DNA. When excised, they may carry bacterial DNA sequences with them.
In rDNA technology, chemical methods include the calcium chloride method, where DNA mixed with positively charged calcium forms a complex, and host cells take up DNA through heat shock. Lipofection uses liposomes that merge with the cell membrane.
Physical methods include electroporation, where transient micropores are created on the membrane by mild electric current. Microinjection introduces DNA directly into the nucleus using specialized apparatus. The biolistic method uses a gene gun to bombard cells with microscopic particles (gold, nickel, tungsten) coated with foreign DNA at high velocity.
Explanation
This answer covers both natural modes of DNA transfer (transformation, transduction, conjugation) as mentioned in the textbook context, as well as the artificial methods used in rDNA technology (chemical and physical methods). Key terms like transformation, transduction, bacteriophages, electroporation, lipofection, microinjection, and biolistic method have been highlighted as per NCERT conventions.