If yeast could sing, it might sound something like this. This single-celled fungus--for which we should give thanks for bread, beer, and wine--can reproduce in several ways. Most of the time, it produces buds that eventually split off as free-living cells of their own. Its daughters are identical to itself, carrying the same two sets of chromosomes. Sometimes, however, life get rough for yeast, and they respond by making spores, each with only one set of chromosomes. Later, when times get better, the spores can germinate. In some cases the yeast cells that emerge just grow and divide. But they can also have sex. One yeast cell merges with another one, combining their DNA to produce a new yeast cell with two sets of chromosomes.
What makes yeast sex especially interesting is that the cells communicate with each other first. A yeast cell produces a pheromone that can cause another ...
