All are capable to grow in lactose medium . In presence of lactose the repressor gets inactivated and transcription continues. Here all mero diploids have functional B- galactosidase (Z) and permease gene (Y) Solution All are capable to grow in lactose medium . In presence of lactose the repressor gets inactivated and transcription continues. Here all mero diploids have functional B- galactosidase (Z) and permease gene (Y).