Question

If a recombinant DNA bearing gene for resistance to antibiotic ampicillin is transferred to E.coli cells, the host cells become transformed into ampicillin resistant cells. If such bacteria are transferred on agar plates containing ampicillin, only transformants will grow and the non-transformed recipient cells will die. The ampicillin-resistant gene in this case is called as _________________.
A. Selectable marker
B. Recombinant protein
C. Cloning site
D. Chemical scalpels

Answer 1

Hint: The term biotechnology can be concertised to the use of living organisms or their products to modify human health and the human environment. But today with the advancement, it is used in a restricted way to refer only to processes which use genetically modified organisms to achieve the same on a larger scale.

Complete answer:
The ligation of alien DNA is made possible at a restriction site present in one of the two antibiotic resistance genes. For example, you can ligate a DNA which is unknown that is foreign DNA at the BamHI site of tetracycline resistance gene in the vector PBR322. The recombinant plasmids that are now developed will now be free from tetracycline resistance due to insertion of foreign DNA but can now also be selected out from non-recombinant ones by plating the transformant on ampicillin-containing medium.
Now let us gather information about given options :-
Selectable marker :- Helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. Mostly , the genes that show resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E.coli.
Recombinant protein:- any – protein that encodes for the gene expression in a heterologous host is termed as recombinant protein. These proteins are prepared with desirable characters and are not used to identify antibiotic resistance genes
Cloning site :- In the process to link and combine the alien DNA, the vector should have very low , preferably single, recognition sites for the commonly used restriction enzymes. Occurrence of more than one recognition site within the vector will generate several fragments, which will complicate gene cloning.
Chemical scalpels :- restriction enzymes are also called chemical scalpels. Restriction enzymes perform as chemical knives to cut genes (= DNA) into defined fragments. These may then be used To determine the order of genes on chromosomes.
So, the correct answer is “Option A”.

Note: The normal E.coli cells do not carry resistance against any of the antibiotics. Also, the gene lac Z coding for B-galactosidase enzyme may also be used as a selection basis. This enzyme utilises its substrate to produce a blue-coloured product. Therefore, the substrate for B-galactosidase is chromogenic (colour producing).