Question

Two weeks ago, you received three unknown yeast strains. One was lys- (it cannot synthesize its

own lysine) while the other two were LYS+. Because they were LYS+, they should be sensitive

to high levels of aminoadipate (AA) before spontaneous and/or induced mutations occur that

may allow some cells to become AA resistant. The two LYS+ strains differ in the rate at which

they accumulate mutations. Two weeks ago, you replica plated these strains onto YPD (enriched

medium), -lys (lacking lysine), and AA (high aminoadipate) plates.

1. Which strain(s) do you expect will grow on the –lys plate?
2. Which strain(s) do you expect will grow the best on the AA plate?
3. You may discover that one LYS+ strains grows less well than the other on the UV-irradiated
side of a YPD plate. What is a plausible genetic mechanism for this result?
4. Propose a mechanism to explain how some cells from the LYS+ strains could grow on the
UV-irradiated side of the AA plate.
5. Propose a mechanism to explain how some cells from the LYS+ strains could grow on the
NON UV-irradiated side of the AA plate.

Answer 1

Step-by-step explanation:

1) The strains LYS+ will be able to survive and grow on -lys plates because they are the only strains able to survive on medium without lysine;

2) The strain -lys will be able to survive at AA plate;

3) The genetic mechanism for the result is that some mutation caused by the UV light made one of the LYS+ strain plates to grow better because it became AA resistant;

4) The mutation caused by UV light probably inactivaded the genes responsible for the synthesis of lysine;

5) There is some level of tolerance by which some cells can survive high levels of AA, that way some cells from the pool of LYS+ strain may survive the AA plate