Question

Alternate selectable markers have ability to differentiate recombinants from non-recombinants due to the

• A. inactivation of the enzyme β-galactosidase
• B. both B and C
• C. inactivation of the recombinants DNA
• D. insertional inactivation

Answer 1

The correct option is B both B and C

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.

Alternate selectable markers have the ability to differentiate transformants from non-transformants by insertional inactivation of the enzymes.

For example, insertional inactivation of the β−galactosidase gene.

Mechanism of action of alternate selectable marker is as follows:

• An alternate method to select transformants and non transformants is by the process of insertional inactivation.
• In this method the gene of interest is ligated within a gene that codes for specific proteins like enzyme β-galactosidase.
• This insertion will inactivate the gene resulting in the absence of the production of the enzyme.
• In such cases, the recombinants will produce white colonies while the non-recombinants will produce blue colonies in the presence of chromogenic substrates.
• This makes it easy to identify recombinants and non-recombinants

Hence the correct option is
d. both B and C