In blue-white selection what does a blue colony generally indicate?

Correct answer: Non-recombinant vector without the target DNA insert

In blue-white selection, an intact lacZα region allows production of functional β-galactosidase, which cleaves X-gal and produces a blue colony. Thus, a blue colony generally indicates that the target DNA insert has not been inserted into the lacZ region, so the vector is non-recombinant. In contrast, an insert disrupts lacZα and usually gives a white colony. Exam tip: blue colony = active lacZ = usually no insert.