In molecular cloning, Blue-white screening is used for -
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.
To screen for recombinant vectors
To detect gene mutations
To identify desired chromosomal DNA insert in plasmid vectors
To detect host DNA in situ