Why are Plasmids and viruses used as vectors?

Transformation of bacteria plasmids are one of the easiest ways to demonstrate and test hypotheses about genetic transformations in laboratory conditions due to the ease of performing the procedure and relative quickness of obtaining results. DNA can be taken into the bacterium by subjecting the a competent cell to heat shock which makes the plasma membrane more fluid. (A bacterial cell may need to be treated with a chemical, ie) CaCl2 in E. coli, in order to become competent, or have enhanced ability for DNA uptake). The foreign DNA, or plasmid, will insert itself into the DNA of the bacterium. Bacterial cells have relatively few genes, compared to other organisms. Bacteria replicate frequently and will therefore express a phenotype in a reasonable amount of time. Only some competent cells will become transformed. This factor is expressed as transformation efficiency, which is defined by (# of transformants obtained)/(# of total cells).