How do Antibiotic Resistance Genes function as selectable marker or helps in selection of transformed recombinant colonies?

What are selectable markers? How are antibiotic resistance genes used as selectable markers?

Let’s begin with selectable marker

What is a Selectable marker in a vector?

Selectable marker is a region or gene sequence (here for Antibiotic resistance) of the vector that helps in selection of recombinant colonies that contain our gene of interest.

You can also watch our video on Selectable markers at the end of this post for easy understanding.

Let’s take an example to understand this concept

An example is the use of pBR322, which has genes that encodes polypeptides which confer resistance to ampicillin and tetracycline antibiotics. That means a bacterium with this vector can grow both tetracycline and ampicillin containing medium.

In the given example (figure above), we have inserted our gene of interest in the tetracycline gene coding region. So that, tetracycline resistance gene is no more functional. This process is called insertional inactivation.

What is Insertional inactivation?

Inactivation of a gene upon insertion of another gene within its gene sequence.

The inserted gene disrupts continuity of the gene sequence, thereby making it inactive or non-functional.

Insertional inactivation helps in the selection of recombinant colonies. Recombinant colonies with desired gene inserted at tetracycline coding region can grow only in ampicillin containing medium, whereas transformed colonies with unchanged vector can grow in both tetracycline and ampicillin medium.  We can select the recombinant colonies by comparing the position of the colonies after replica plating with the master plate. (Understand More on replica plating)

Watch this 5-minute video for better understanding.

Thank you so much:)