The cultivars released since 1980 were either genetically identical or very similar to the first hybrid (Sonnenberg et al., 2011). The main reason for the lack of introduction of new cultivars lies in the typical life cycle of the button mushroom. We have carried out a more detailed analysis of its meiosis as has been done so far to make clear what the obstacles are in breeding and also to explain the very narrow genetic base of almost all cultivars of the white button mushroom grown worldwide.