Questions: What hypothesis was being tested with the Aformin strain? Formin causes shmoo formation in mating yeast. Formin is required for the signal transduction pathway leading to shmoo formation. Phosphorylation of formin is required for the signal transduction pathway leading to shmoo formation. Mating factor is required to start the signal transduction pathway leading to shmoo formation.

The answer is the third one: Phosphorylation of formin is required for the signal transduction pathway leading to shmoo formation.

Explanation for each option:

1. Formin causes shmoo formation in mating yeast.
   This hypothesis suggests that formin directly causes shmoo formation, but it does not specify the mechanism, such as phosphorylation, which is a more specific hypothesis.

2. Formin is required for the signal transduction pathway leading to shmoo formation.
   This hypothesis indicates that formin is necessary for the pathway but does not specify the role of phosphorylation, which is a more detailed aspect of the hypothesis being tested.

3. Phosphorylation of formin is required for the signal transduction pathway leading to shmoo formation.
   This is the most specific hypothesis, focusing on the phosphorylation of formin as a necessary step in the signal transduction pathway for shmoo formation. Testing the Aformin strain likely involves examining whether the lack of phosphorylation affects the pathway.

4. Mating factor is required to start the signal transduction pathway leading to shmoo formation.
   This hypothesis is about the initiation of the pathway by the mating factor, not specifically about the role of formin or its phosphorylation.

In summary, the hypothesis being tested with the Aformin strain is that phosphorylation of formin is required for the signal transduction pathway leading to shmoo formation.