Practice question

Scorable markers produce easily detectable phenotype such as color or fluorescence upon expression, useful for screening recombinants independent of selection pressure. Examples include lacZ producing blue product from X-gal, green fluorescent protein emitting green fluorescence, and luciferase generating bioluminescence catalyzing luciferin oxidation. Tetracycline resistance TetR encodes membrane efflux pump conferring resistance to tetracycline, allowing only selective growth but not visual scoring of insertional events without replica plating. It functions strictly as selectable marker for plasmid retention, not for scoring recombinant status through observable pigment or light emission.