Question

A gene whose expression helps to identify transformed cell is known as

• A. Plasmid
• B. Selectable marker
• C. Vector
• D. Structural gene

Answer 1

The correct option is B Selectable marker

Vector
Vectors are the DNA molecules that can carry a foreign DNA fragment to be cloned. For example, pBR 322 is a cloning plasmid vector that is used to transfer a DNA of interest into a host cell such as Escherichia coli to form multiple copies.

Plasmids
Plasmids are circular, extranuclear, double stranded, self replicating DNA molecules that are used as vectors for small fragments of DNA. Usually most plasmids carry DNA inserts of about 15 kbp in size.

Structural gene
Structural gene is a gene that codes for enzymes or structural proteins.

Selectable marker
Selectable marker is a gene in a vector that helps in the selection of transformants (host cells which have successfully taken up the foreign DNA) and non-transformants (cells which have not taken up the vector DNA).
For example, antibiotic resistance genes in the vector act as selectable markers because they confer antibiotic resistance to the transformants while the non-transformants remain susceptible to antibiotics.

Final answer
d. Selectable marker.