When making insulin why is it necessary to introduce a gene for antibiotic res

A selectable marker is a gene introduced into a cell, especially a bacterium or to cells in culture, that confers a trait suitable for artificial selection. They are a type of reporter gene used in laboratory microbiology, molecular biology, and genetic engineering to indicate the success of a transfection or other procedure meant to introduce foreign DNA into a cell.

Selectable markers are often antibiotic resistance genes; bacteria that have been subjected to a procedure to introduce foreign DNA are grown on a medium containing an antibiotic, and those bacterial colonies that can grow have successfully taken up and expressed the introduced genetic material.

Normally the genes encoding resistance to antibiotics such as ampicillin, chloroamphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E.coli. Modus Operandi- The non recombinants are separated from recombinants. i.e. A r-DNA is introduced in a bacteria, some bacterias are successfully transformed some remains non-transformed. When grown on medium containing ampicillin bacteria die due to lack of ampicillin resistance. The position is later noted on nitrocellulose paper and separated out to move them to nutrient medium for mass production of required product.