Question

Choose the false statement.

• A. More than one copy of the same recognition site within a vector can complicate gene cloning
• B. In pBR322, only one selectable marker is present
• C. The technique of PCR was developed by Kary Mullis
• D. Retroviruses when infects animal cells have the ability to transform normal cells into cancerous cells

Answer 1

The correct option is B In pBR322, only one selectable marker is present

The plasmid DNA molecule, pBR322, was the first artificial cloning vector constructed by Bolivar and Rodriguez. Here, p stands for plasmid, BR for Bolivar and Rodriguez and 322 for the number given to this plasmid. It has two antibiotic resistance genes which act as selectable markers - ampicillin resistance gene and tetracycline resistance gene.

Cloning site is the recognition site in DNA at which the restriction enzyme binds and makes a cut. Foreign DNA can be inserted in those sites after the cut. It is better to have a single recognition site for restriction enzymes used. Presence of more than one recognition site for a particular restriction enzyme within the vector will generate several fragments, which will make gene cloning complicated.

PCR stands for polymerase chain reaction which was developed by Kary Mullis. In this reaction, multiple copies of a specific sequence of DNA can be synthesised in vitro. This process uses two sets of primers (chemically synthesised oligonucleotides that are complementary to certain regions of DNA) and the enzyme Taq DNA polymerase which extends the primers using the deoxyribonucleotides provided in the reaction.

Retroviruses have the ability to transform normal animal cells into cancerous cells. Retroviruses have also been disarmed and are now used to deliver desirable genes into animal cells.