Foreword, M. Ptashne 1. Why Read a Book about Yeast? 2. Yeast Cell Types 3. Master Regulatory Transcription Factors Control Cell Type 4. Making and Secreting Cell Type-specific Signals 5. Detecting and Responding to a Signal 6. How Division of a Single Cell Can Produce Two Cell Types 7. Gene Silencing in the Control of Cell Type 8. Controlling Cell Polarity 9. Evolution of Cell Type Determination Index