Practice question

Markers distinguishing recombinant from non-recombinant clones can be scorable reporters whose phenotype alters upon insertional inactivation. Green fluorescent protein provides intrinsic fluorescence detectable under UV without exogenous substrate, making it convenient for colony screening. Vectors containing GFP transcriptional fusion show fluorescence when empty; cloning into gfp disrupts chromophore formation, extinguishing signal in recombinants. Origin of replication governs replication, while AmpR and TetR are selectable markers conferring survival on antibiotics but not visual distinction between recombinant and empty plasmid states. Thus GFP offers rapid optical differentiation.