Practice question

Scorable markers permit phenotypic discrimination of clones without killing non-recombinants, unlike selectable markers that allow growth only of transformants. LacZ encoding β-galactosidase is a classic scorable system; its intact product hydrolyzes chromogenic X-gal into blue precipitate. When foreign DNA inserts within lacZα, α-complementation fails. Colonies remain colorless, enabling visual scoring. Antibiotic resistance genes AmpR and TetR and origin of replication Ori provide selection or maintenance but do not produce a directly scoreable colorimetric or luminescent signal for screening recombinant status.