Chapter 11, Problem 40P

Common baker’s yeast ( $\text{Saccharomyces cerevisiae}$) is normally grown at $\text{37°C}$, but it will grow actively at temperatures down to approximately $\text{25°C}$. A haploidculture of wild $\text{-}$ type yeast is mutagenized with EMS.Cells from the mutagenized culture are spread on a complete $\text{-}$ medium plate and grown at $\text{25°C}$. Six colonies $\left(\text{1 to 6}\right)$ are selected from the original complete $\text{-}$ medium plate and transferred to two fresh complete $\text{-}$ medium plates. The new complete plates (shown below) are grown at $\text{25°C and 37°C}$. Four replica plates are made onto minimal medium or minimal plus adenine from the $\text{25°C}$ complete $\text{-}$ medium plate. The new plates are grown at either $\text{25°C and 37°C}$ and the growth results are shown.

a. Which colonies are prototrophic and which are auxotrophic? What growth information is used to makethese determinations?

b. Classify the nature of the mutations in colonies $\text{1, 2, and 5}$.

c. What can you say about colony $\text{4}$?