Question

discuss the process and principle involved for screening/selection of hosts (last stage of cloning) containing the intended recombinant plasmid.

Answer 1

Screening or selection of the transformed recombinant cells can be done by a lot of techniques. Using selectable marker genes or reporter genes are some widely used methods to select the recombinant cell.

Selectable marker genes :

These are particular genes that are present on the vector that is integrated with the gene of interest to be recombined with the host cell. These marker genes are the genes for specific enzymes that the hst cell normally cannot synthesize in absence of the enzyme from the medium. If the recombination did occur, the host cell recombined will be able to produce the respective enzyme whose gene is the selectable marker. The cells that aren't recombined will not grow on the media at all. This way the recombined cell can be selected very easily.

Reporter gene :

It is almost the same as the selectable marker genes but here there are no dead cells. The reporter gene will have a chromophore specifically that will distinguish the recombined cell from the non recombined ones. So in that way the recombined cells can be differentiated from the non recombinant cells.