Answer:
The correct answer is "mutations in the lac operon or in the promoter region".
Explanation:
The lac operon es a series of genes that are translated and expressed simultaneously, allowing the cell to metabolize lactose when glucose is absent. The E.coli cultures that failed to grow in the presence of only lactose, could have a mutation that affects the lac operon. This mutation could be present in the promoter region or in the lac operon itself, which will result in the absence of lac operon transcription or in the transcription of one or more non active protein, respectively.
The mutation(s) that could explain why the E. coli cultures failed to grow only in the presence of lactose is: mutations in the lac operon or promoter regions.
Recall:
Thus, the possible reason that would make the E. coli cultures not to grow in the presence of only lactose would most like suggest a mutation which might have occurred in the lac operon or promoter region.
Therefore, the mutation(s) that could explain why the E. coli cultures failed to grow only in the presence of lactose is: mutations in the lac operon or promoter regions.
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