Zoology - Biotechnology - Principles and Processes Question with Solution | TestHub

Screenable marker, visual marker or reporter gene generates a product that can be detected. It is used in confirming transformation, determining transformation efficiency and monitoring gene expression. 

The most common example is the lac Z gene of E. coli. Lac Z gene acts as a screenable marker in the presence of X-gal because its expression is readily quantitated by the intensity of the blue colour that is generated.

Lac Z (reporter gene) $\to$ $\beta$-galactosidase (gene product) $\to$X-gal (substrate) $\to$1. Blue colonies  (non-transformants) 2. White colonies (transformants)