Chapter 12, Problem 11P

Two different mutations are identified in a haploid strain of yeast. The first prevents the synthesis of adenine by a nonsense mutation of the $\text{ade-1}$ gene. In this mutation, a base $\text{-}$ pair substitution changes a tryptophan codon (UGG) to a stop codon (UGA). The second affects one of several duplicate tRNA genes. This base $\text{-}$ pair substitutionmutation changes the anticodon sequence of a ${\text{tRNA}}^{\text{Trp}}$ from $\text{3'-ACC-5'}$ to $\text{3'-ACU-5'}$.

Do you consider the first mutation to be a forward mutation or a reversion? Why?

Do you consider the second mutation to be a forward mutation or a reversion? Why?

Assuming there are no other mutations in the genome, will this double $\text{-}$ mutant yeast strain be able to grow on minimal medium? If growth will occur, characterize the nature of growth relative to wild type.