Question

A bacterial strain can grow on rich medium (which contains all the amino acids, vitamins, and a variety of carbon sources) but not on minimal medium or on minimal medium supplemented with leucine. Assuming that there is no mutation in other loci, what could be the genotype(s) of this bacterial strain with respect to the arg and leu loci ? A. arg–leu– or arg–leu+ B. arg+leu– C. arg+leu– or arg–leu+ D. arg–leu+ E. arg–leu– or arg+leu–

Answer 1

Answer:

The correct answer is option C. "arg+leu– or arg–leu+".

Explanation:

This bacteria is not able to growth on minimal medium or minimal medium  supplemented with leucine. This means that the bacteria needs external supplementation of amino acids to growth, either arginine or leucine. Therefore, this bacteria can have the genotypes of arg+leu– or arg–leu+, meaning that the bacteria is able to synthesize either of two amino acids, but not both, because if that was the case the bacteria would be able to growth on minimal medium.