Practice question

Auxotrophs carry mutation in a gene encoding enzyme in biosynthetic pathway, blocking synthesis of specific growth factor such as histidine, leucine, arginine, or tryptophan. Unlike prototrophs that produce everything, auxotrophs need exogenous supplement of that metabolite added to medium to grow. They are isolated after mutagenesis and used to pinpoint pathway steps and map genes. Reversion to prototrophy via back-mutation or recombination confirms gene identity. Conditional growth requirement makes auxotrophs ideal for selection in conjugation, transformation, and complementation experiments for pathway dissection.