Final answer:
This partial diploid strain of E. coli will never make beta-galactosidase. The correct option is c.
Step-by-step explanation:
This partial diploid strain of E. coli has the lacI+ gene, which produces the lac repressor protein, and the O+ gene, which allows for normal binding of the repressor to the operator. It also has the lacZ+ gene, which produces functional beta-galactosidase, and the lacY- gene, which prevents the production of lactose permease.
Under normal conditions, this strain will not make beta-galactosidase because it has a lacY- mutation. Lactose permease is necessary for the transport of lactose into the cell, and without it, lactose cannot be converted to allolactose, which is the inducer of the lac operon.
Therefore, this strain will not make beta-galactosidase even when lactose is present. So the correct answer is C. never. The correct option is c.