Yeasts make bread, wine, beer and other products for us and play a central role in current biological research. The video describes the life cycle of homothallic yeast strains and heterothallic ones which are commonly used in genetic laboratories. The developmental stages - e.g. budding, conjugation, zygote formation and germination, ascus formation, sporulation and ascus germination - are presented using time-lapse cinemicrography. The spontaneous mating type switch in the second budding generation of homothallic strains is demonstrated for the first time on this video, employing time-lapse techniques. The most important features of the live cycle are summarized diagramatically. The video is aimed at scientists experimenting with yeasts, but is suitable also for teaching at universities and if introduced by a teacher, schools at an advanced level.