Chapter 12, Problem 31P

A wild $\text{-}$ type culture of haploid yeast is exposed to ethyl methanesulfonate (EMS). Yeast cells are plated on a complete medium, and $\text{6}$ colonies (colonies numbered $\text{1}$ to $\text{6}$) are transferred to a new complete medium plate for further study. Four replica plates are made from the complete medium plate to plates containing minimal medium orminimal medium plus one amino acid (replica plates numbered $\text{1}$ to $\text{4}$) with the following results:

a. Identify the colonies that are prototrophic (wild type). What growth information leads to your answer?

b. Identify the colonies that are auxotrophic (mutant). What growth information leads to your answer?

c. Identify any colonies that are ${\text{his}}^{\text{-}}{\text{,arg}}^{\text{-}}{\text{,leu}}^{\text{-}}$.

d. For colonies $\text{1}$, $\text{3}$, and $\text{5}$, write “ $\text{+}$” for the wild-type synthesis and “ $-$” for the mutant synthesis of histidine and leucine.

e. Are there any colonies for which genotype information cannot be determined? If so, which colony or colonies?