Question

Which of the following is most difficult to detect?

• A. Auxotrophic mutation
• B. Lethal mutation
• C. Recessive non-lethal mutation
• D. Dominant mutation

Answer 1

The correct option is C Recessive non-lethal mutation

Auxotrophs are the mutant cells that are incapable of utilizing certain nutrients or synthesizing certain compounds and hence they can grow on minimal media plus the specific growth supplement for which they are mutant. Auxotrophic mutations can be detected by culturing the mutants on minimal media with or without growth supplements; the auxotrophs will not grow on minimal media. Lethal mutations are the one that causes premature death of the individual which are detected by using balanced lethal stock that carries recessive lethal heterozygotes; the recessive lethal homozygous genotype is not observed in the progeny. Dominant mutations are the one that expresses themselves in heterozygotes; thus a cross between two pure breeding genotypes produces a different phenotype in F${}_1$ hybrid. Recessive non-lethal mutations are suppressed by the presence of wild-type dominant alleles and are expressed only in recessive homozygotes; their detection needs development of hybrid line by the cross between two pure varieties followed by selfing of hybrid to obtain recessive homozygotes. Thus, they are most difficult to detect. The correct answer is C.