an ecoli strain is chromosomally lacZ- but a wildtype copy of entire lac operon is present on an F' plasmid which in turn has a penicillin resistant gene.now when ecoli is grown without penicillin,some colonies are penicillin sensitive and lac+.how? could be explained by an ecoli strain is chromosomally lacZ- but a wildtype copy of entire lac operon is present on an F' plasmid which in turn has a penicillin resistant gene.now when ecoli is grown without penicillin.
