In recombinant DNA technology, a selectable marker is a gene sequence included within a cloning vector. Its primary purpose is to differentiate between host cells that successfully took up the vector (transformants) and those that did not (non-transformants). For example, antibiotic resistance genes (like ampicillin or tetracycline resistance in plasmid pBR322) act as selectable markers. When grown on an antibiotic-infused medium, only the transformants survive and grow, allowing researchers to effortlessly eliminate non-transformants.

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