Q41 - Complementation Analysis of the Arginine Biosynthesis Pathway

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

Gene Interactions: Epistasis & Complementation Analysis

In mold/mould, synthesis of the amino acid arginine requires prior conversion of a precursor to ornithine, which is then converted to citrulline, which further is converted to arginine. Each of these three steps is catalyzed by a separate enzyme, coded for by a separate gene (Fig.). A, biosynthetic pathway for arginine in mold; B, experimental set-up to confirm pathway; dark brown stripe denotes mold growth. The wild type grows on minimal medium, while the mutants only grow with addition of specific nutrients.

Figure 1. Figure 1.

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

A. Class III mutants may have mutations in more than one gene involved in the pathway

B. Class I mutants lack activity of all three enzymes

C. Mutants, lacking both enzyme A and C, will grow if ornithine and citrulline are both added

D. Assuming that an inhibitor to enzyme B is added to the wild type, gene B will be inactivated

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Question reproduced from IBO 2015, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)