What should be done if expected restriction bands are not obtained?

Correct answer: Further verify or re-screen the clone

The direct answer is A: further verify or re-screen the clone. Restriction analysis cuts DNA at particular recognition sequences, so a known clone should produce an expected band pattern on a gel. The reasoning is: digest the clone DNA; separate fragments by size; compare observed bands with the predicted pattern; if they do not match, do not accept the clone immediately; repeat or use another confirmation method such as a new restriction digest, colony PCR, sequencing, or checking for rearrangement. Option A is correct because an unexpected pattern may indicate a wrong clone, an incomplete digest, contamination, or rearrangement, so verification is necessary. Option B is unsafe because accepting unchecked data can lead to a false conclusion. Option C is inappropriate and hazardous; DNA must never be tasted. Option D is scientifically and ethically unacceptable because engineered hosts must be handled under proper containment, not released. A useful cue is: unexpected bands mean “stop, check, confirm,” not “accept.”