Vectors frequently expresses beta-galactosidase (lacZ) gene at the cloning
sites. Insertion may disrupt the lacZ gene, thus generating white clonies
on a X-gal plate.
1. Prepare X-gal plates.
2. Spread cells on the X-gal plates.
3. Incubate at 37 °C for overnight.
4. Blue clonies should appear overnight.
5. If the color is light, store plates in 4 °C, blue clonies get darker over time in 4 °C.