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Q33 - Complementation and Dominance in lac Operon Merodiploids

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Gene Regulation: Prokaryotic

Mr. Long had ten strains of Escherichia coli with different mutations in their lac operon. Analyzing their DNA, he found that each strain is one of five mutation types: lacZ-, lacY-, lacI-, lacIs (the repressor LacI can bind to the operator but cannot bind to the inducer), or lacOc (the mutated operator lacOc cannot be bound by the repressor). Mr. Long also knew that strain number 6 is a lacZ- mutant. Mr. Long isolated DNA containing the lac operon from each strain (donor) and transformed it into other strains, thus making the strain merodiploid (recipient). Thereafter recipient strains were cultured on minimal medium that contained lactose as the only carbon source. Growth of the strains was recorded in a table (+ means the strain is growing, - means the strain is not growing).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Strain number 7 is a lac Z mutant.
B. Strain number 3 is a lac Y mutant.
C. Strains number 2 and 4 are of the same mutation type.
D. If strain number 5 receives DNA from itself, the transformed bacteria cannot grow.
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Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)