Chapter 12, Problem 40P

Two haploid strains of fungus are fused to form a diploid that produces eight-celled asci. Fungus strain A has the genotype $\text{+ ade1 his2,}$ and strain B is $\text{a++}$. The three genes are linked and occur in the order given.

a. The alleles at the A gene locus are determined in an ascus, and the order is $\text{aaaa + + + +}$. Write the genotype for all three genes that you expect to find most commonly.

b. One ascus from the diploid is of the following type:

$\begin{array}{l}\text{+ ade1 his2}\hfill \\ \text{+ ade1 his2}\hfill \\ \text{+ ade1 his2}\hfill \\ \text{+ ade1 his2}\hfill \end{array}$

$\begin{array}{l}\text{a ade1 +}\hfill \\ \text{a + +}\hfill \\ \text{a + +}\hfill \\ \text{a + +}\hfill \end{array}$

Explain the events that produced this ascus.

c. One ascus from the diploid is of the following type:

$\begin{array}{l}\text{a + +}\hfill \\ \text{a + +}\hfill \\ \text{a + his2}\hfill \\ \text{a + his2}\hfill \\ \text{+ ade1 his2}\hfill \\ \text{+ ade1 his2}\hfill \\ \text{+ ade1 his2}\hfill \\ \text{+ ade1 his2}\hfill \end{array}$

Explain the events that produced this ascus.