K17. Which of the following mismatch corrections will create a tetrad in which three of the spores are Leu+ and one of the spores is Leu- (3 LEU2: 1 leu2)? Two strains of the yeast, S. cerevisiae, are crossed. One has the genotype ABC and the other abc. Five sets of the resultant tetrads are shown below. In which set did a gene conversion event occur? A. abc, aBc, AbC, aBC B. abc, abc, ABC, ABC C. aBc, aBc, AbC, AbC D. abC, abc, ABc, ABC E. Abc, Abc, aBC, aBC K18. You have isolated two mutant strains of S. cerevisiae that are unable to grow in the absence of added leucine. Diploids made with these two strains are also unable to grow without leucine. The two strains are mated and analysis of the progeny reveals that spores that can grow in the absence of leucine are recovered at a low frequency. What is the most likely explanation for these observations? A. B. C. D. The two mutations are in different, but closely linked genes.

An industry consists of two rms which can either colludeor com-

petein each period. The per-period payo¤s of doing either are as follows:

Firm 1

Firm 2 Collude Compete

Collude $50 $50 -$10 $75

Compete $75 -$10 $45 $45

If the rms initially collude, either of them can earn $25 extra by cheating on the agree-

ment and competing instead. The other rm can retaliate, however, by refusing to collude

in subsequent periods.

For how many periods would such retaliation have to last to deter cheating if the interest

rate is 0%, so that the rms do not discount future prots?

3