In molecular cloning, Blue-white screening is used for -
To screen for recombinant vectors
To detect gene mutations
To identify desired chromosomal DNA insert in plasmid vectors
To detect host DNA in situ
Screening for selecting the cells with vector DNA containing the desired insertional DNA sequence can be done by :


Antibiotic resistance markers:- Allow only cells in which the vector has been transfected to grow.
Blue-white screening:- It is based on lac operon. The hydrolysis of X-gal by β-galactosidase cause blue colour in colonies & indicates that colonies contain the unligated vector. Whereas, white colonies indicate insertion of foreign DNA and loss of cells ability to hydrolyse marker.
PCR, restriction fragment analysis and DNA sequencing:- Confirmatory methods.