Final answer:
Strains a and d of E. coli will synthesize lacZ in the presence of lactose.
Step-by-step explanation:
The correct answer is:
a. lacIs lacP- lacO+ lacZ+ lacY+/lacI+ lacP+ lacO+ lacZ- lacY+
d. lacI- lacP+ lacO+ lacZ+ lacY+
These two E. coli strains will synthesize lacZ in the presence of lactose. The lacI gene in strain a produces a mutant repressor protein that cannot bind to the operator DNA, allowing for transcription of the lac operon genes (lacZ). The lacP mutation interferes with the RNA polymerase binding to the promoter, resulting in low transcription of the lac operon genes. However, the presence of lactose can overcome this mutation, allowing for lacZ synthesis.
Similarly, in strain d, the lacI gene produces a repressor protein that cannot bind to the operator DNA, leading to transcription of the lac operon genes (lacZ). The lacP mutation does not affect the ability of RNA polymerase to bind to the promoter. Therefore, the presence of lactose is sufficient to induce lacZ synthesis.