Final answer:
Mutations in yeast cells allowing for survival in the presence of toxic levels of hydrogen peroxide occur randomly, either before or after exposure to the hydrogen peroxide.
Step-by-step explanation:
The Luria-Delbruck fluctuation test involves exposing yeast cells to toxic levels of hydrogen peroxide to study the occurrence of mutations.
Based on the test, mutations in yeast cells allowing for survival in the presence of hydrogen peroxide are random. This means that mutations can occur before or after exposure to hydrogen peroxide, and their occurrence is not necessarily adaptive or immediate.