AP BIOLOGY

Detailed explanation-1: -Screening can be based on detecting the DNAsequence of the. cloned gene. A copy of a gene that has been combined with a plasmid and placed into a bacteria cell., detecting a protein that the gene encodes, or the use of linked DNA markers.

Detailed explanation-2: -For screening the clones containing recombinant DNA, a chromogenic substrate known as X-gal is added to the agar plate. If -galactosidase is produced, X-gal is hydrolyzed to form 5-bromo-4-chloro-indoxyl, which spontaneously dimerizes to produce an insoluble blue pigment called 5, 5’-dibromo-4, 4’-dichloro-indigo.

Detailed explanation-3: -One solution is to identify the desired recombinants directly with the help of the marker genes, or indirectly by the technique of colony-hybridization using a radioactive probe of the specific DNA or RNA. Another approach is to use a pre-selected DNA segment containing the desired gene for cloning.

Detailed explanation-4: -Once a library is constructed it is screened for a particular gene of interest. Screening is based on homology between a probe and one of the clones in the library. The probe is normally a nucleic acid that has some sequence homology to the gene that is represented in the library.