An antibiotic resistance gene in a vector usually helps in the selection of :

Transformed bacterial cells

(b) transformed bacterial cells

An antibiotic-resistance gene in a vector is used as a selectable marker to help in the selection of transformed bacterial cells. During the gene cloning process, the vector containing the antibiotic resistance gene and the foreign DNA (recombinant DNA) is introduced into bacterial cells. Most bacterial cells will not take up the vector, and those that do without incorporating the foreign DNA will not survive in the presence of the antibiotic.

However, the transformed bacterial cells that successfully incorporate the recombinant DNA into their genome will also acquire the antibiotic resistance gene. When these cells are grown on a medium containing the specific antibiotic, only the transformed cells will be able to survive since they possess the resistance gene. Non-transformed cells, lacking the antibiotic resistance gene, will be killed by the antibiotic.

By selecting for the survival of cells with antibiotic resistance, researchers can identify and isolate the bacterial cells that have successfully taken up and expressed the foreign DNA, which are the desired recombinant bacterial cells.