Lab - Influence of UV irradiation on a yeast culture

Extract from the Official Bulletin:
Genetic variation and DNA mutation (1-A)

Scientific problem:
During DNA replication, errors can occur, the frequency of which can vary depending on external agents. These errors can persist to result in a mutation that contributes over time to genetic variability.
Certain environmental factors (UV, benzene) lead to an increase in these mutations.
How can we highlight and analyze the influence of these factors on a yeast culture?

Procedure:
A population of the yeast S.cerevisiae ADE2 is exposed to a progressive level of ultraviolet radiation.
The effects of this exposure are then measured:
- By counting the number of viable colonies,
- By restoring a wild-type phenotype (seen in seconds).

Why use the yeast S.cerevisiae ADE2?
With this strain, we can observe the consequences of certain mutations.
The yeast S.cerevisiae ADE2 is a yeast that has undergone a mutation in its Adenine biosynthesis pathway, making it auxotrophic, meaning it is unable to synthesize this compound.
In the absence of a sufficient amount of Adenine in the environment, the yeast accumulates an intermediate product of pink color.