Read the passage carefully and answer the given questions.

Recombinant DNA Technology

Asexual reproduction preserves the genetic information, while sexual reproduction permits variation. Traditional hybridization procedures used in plants and animals breeding very often lead to inclusion and multiplication of undesirable genes along with the desired genes. The techniques of genetic engineering, which include creation of recombinant DNA, use of gene cloning and gene transfer, overcome this limitation and allow us to isolate and introduce only one or a set of desirable genes without introducing genes into the target organism.

In Recombinant DNA Technology, what is the role of the "selectable marker gene"?

To help in identification and selection of the host cells that contain the recombinant DNA

The correct answer is Option (3) → To help in identification and selection of the host cells that contain the recombinant DNA  

Origin of replication (ori) is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. In addition to ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating non- transformants and selectively permitting the growth of the transformants. Transformation is a procedure through which a piece of DNA is introduced in a host bacterium. Normally, the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli. The normal E. coli cells do not carry resistance against any of these antibiotics. So, an antibiotic resistance gene in a vector usually helps in the selection of transformed cells.

A selectable marker in genetic engineering serves as a means to identify and distinguish cells that have successfully taken up the foreign DNA (transformants) from those that haven't (non-transformants). It also allows researchers to selectively promote the growth of the transformed cells while inhibiting the growth of non-transformed cells.