Question

Let’s think about mutations in the context of selection and evolution. Normally, random mutations are very rare, but this process can be accelerated by using DNA damaging agents. Imagine you are working with yeast. Normally, high levels of salt kill yeast. However, you are conducting a random genetic screen to find salt-tolerant mutants. You use a DNA damaging agent (like EMS, or UV light) to damage the yeast DNA, then look for growth on plates with salt.
a. Does putting the yeast on salt cause the beneficial mutation? Why or why not?
b. If you screened your mutagenized yeast cell population on caffeine (another substance that normally kills them), could you find caffeine tolerant ones? (assume there is the potential for genetic resistance to caffeine).

Answer 1

a. Does putting the yeast on salt cause the beneficial mutation? Why or why not?

When the logarithmic growth of cells is interrupted by exposure to a 0.5 to 2 Molar salt solution the aueous solution consisting of KCl, NH4Cl, NaCl, MgCl2 are basically mutagenic in yeast .

Stationary phase cells are not mutated by the treatment.

b. If you screened your mutagenized yeast cell population on caffeine (another substance that normally kills them), could you find caffeine tolerant ones? (assume there is the potential for genetic resistance to caffeine).

For normal tolerance to caffiene the sty1 and pap 1 pathways are not necessary, but generally only sty1 is activated by mutation hence making yeast sensitive for caffiene.